<PAGE>   1

   AS FILED WITH THE SECURITIES AND EXCHANGE COMMISSION ON DECEMBER 16, 1999

                                                    REGISTRATION NO. 333-
--------------------------------------------------------------------------------
--------------------------------------------------------------------------------

                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549
                            ------------------------
                                    FORM S-4
                             REGISTRATION STATEMENT
                                     Under
                           THE SECURITIES ACT OF 1933
                            ------------------------
                    Issuer of Senior Notes registered hereby
                         ALLIANT ENERGY RESOURCES, INC.
             (Exact name of registrant as specified in its charter)
                            ------------------------

<TABLE>
<S>                                <C>                                <C>
            WISCONSIN                            6719                            39-1605561
 (State or other jurisdiction of     (Primary Standard Industrial      (I.R.S. Employer Identification
          incorporation)              Classification Code Number)                   No.)
</TABLE>

                                 ALLIANT TOWER
                              200 FIRST STREET SE
                            CEDAR RAPIDS, IOWA 52401
                                 (319) 398-4411
  (Address, including zip code, and telephone number, including area code, of
                   registrant's principal executive offices)

                  Guarantor of Senior Notes registered hereby
                           ALLIANT ENERGY CORPORATION
            (Exact name of registration as specified in its charter)

<TABLE>
<S>                                <C>                                <C>
            WISCONSIN                            6719                            39-1380265
 (State or other jurisdiction of     (Primary Standard Industrial      (I.R.S. Employer Identification
          incorporation)              Classification Code Number)                   No.)
</TABLE>

                           222 WEST WASHINGTON AVENUE
                            MADISON, WISCONSIN 53703
                                 (608) 252-3311
  (Address, including zip code, and telephone number, including area code, of
                   registrant's principal executive offices)

<TABLE>
<S>                                                  <C>
                 EDWARD M. GLEASON                                       Copies to:
 VICE PRESIDENT-TREASURER AND CORPORATE SECRETARY               BENJAMIN F. GARMER, III, ESQ.
          ALLIANT ENERGY RESOURCES, INC.                               FOLEY & LARDNER
            ALLIANT ENERGY CORPORATION                            777 EAST WISCONSIN AVENUE
            222 WEST WASHINGTON AVENUE                           MILWAUKEE, WISCONSIN 53202
             MADISON, WISCONSIN 53703                                  (414) 271-2400
                  (608) 252-3311
 (Name, address, including zip code, and telephone
                      number,
    including area code, of agent for service)
</TABLE>

                            ------------------------
    APPROXIMATE DATE OF COMMENCEMENT OF PROPOSED SALE TO THE PUBLIC: Upon
consummation of the Exchange Offer referred to herein.

    If the securities being registered on this Form are being offered in
connection with the formation of a holding company and there is compliance with
General Instruction G, check the following box.  [ ]

    If this Form is filed to register additional securities for an offering
pursuant to Rule 462(b) under the Securities Act, check the following box and
list the Securities Act registration statement number of the earlier effective
registration statement for the same offering.  [ ]

    If this Form is a post-effective amendment filed pursuant to Rule 462(d)
under the Securities Act, check the following box and list the Securities Act
registration statement number of the earlier effective registration statement
for the same offering.  [ ]
                            ------------------------
                        CALCULATION OF REGISTRATION FEE

<TABLE>
<CAPTION>
-------------------------------------------------------------------------------------------------------------------------
-------------------------------------------------------------------------------------------------------------------------
                                                             PROPOSED MAXIMUM       PROPOSED MAXIMUM
        TITLE OF EACH CLASS OF            AMOUNT TO BE        OFFERING PRICE           AGGREGATE            AMOUNT OF
      SECURITIES TO BE REGISTERED          REGISTERED          PER UNIT(1)           OFFERING PRICE     REGISTRATION FEE
-------------------------------------------------------------------------------------------------------------------------
<S>                                     <C>               <C>                    <C>                    <C>
7 3/8% New Senior Notes due 2009(2)....   $250,000,000             100%               $250,000,000           $66,000
-------------------------------------------------------------------------------------------------------------------------
Guarantees for the New Senior Notes due
  2009(3)..............................        --                   --                     --                  --
-------------------------------------------------------------------------------------------------------------------------
-------------------------------------------------------------------------------------------------------------------------
</TABLE>

(1) Estimated solely for purposes of determining the registration fee.
(2) Calculated pursuant to Rule 457(f) under the Securities Act of 1933.
(3) Pursuant to Rule 457(n) under the Securities Act of 1933, no registration
    fee is required with respect to the guarantees.
                            ------------------------
    THE REGISTRANTS HEREBY AMEND THIS REGISTRATION STATEMENT ON SUCH DATE OR
DATES AS MAY BE NECESSARY TO DELAY ITS EFFECTIVE DATE UNTIL THE REGISTRANTS
SHALL FILE A FURTHER AMENDMENT WHICH SPECIFICALLY STATES THAT THIS REGISTRATION
STATEMENT SHALL THEREAFTER BECOME EFFECTIVE IN ACCORDANCE WITH SECTION 8(A) OF
THE SECURITIES ACT OF 1933 OR UNTIL THE REGISTRATION STATEMENT SHALL BECOME
EFFECTIVE ON SUCH DATE AS THE COMMISSION, ACTING PURSUANT TO SAID SECTION 8(A),
MAY DETERMINE.

--------------------------------------------------------------------------------
--------------------------------------------------------------------------------
<PAGE>   2

     THE INFORMATION IN THIS PROSPECTUS IS NOT COMPLETE AND MAY BE CHANGED. WE
     MAY NOT SELL THESE SECURITIES UNTIL THE REGISTRATION STATEMENT FILED WITH
     THE SECURITIES AND EXCHANGE COMMISSION IS EFFECTIVE. THIS PROSPECTUS IS NOT
     AN OFFER TO SELL THESE SECURITIES AND IT IS NOT SOLICITING AN OFFER TO BUY
     THESE SECURITIES IN ANY STATE WHERE THE OFFER OR SALE IS NOT PERMITTED.

                 SUBJECT TO COMPLETION, DATED DECEMBER 16, 1999

   [ALLIANT ENERGY RESOURCES, INC. LOGO]

                         ALLIANT ENERGY RESOURCES, INC.
                               OFFER TO EXCHANGE
                                ALL OUTSTANDING
                          7 3/8% SENIOR NOTES DUE 2009
                  ($250,000,000 PRINCIPAL AMOUNT OUTSTANDING)
                                      FOR
                        NEW 7 3/8% SENIOR NOTES DUE 2009
                        ($250,000,000 PRINCIPAL AMOUNT)

                             ----------------------

-  We are offering to exchange new registered 7 3/8% Senior Notes due 2009 for
   all of our outstanding unregistered 7 3/8% Senior Notes due 2009.

-  The exchange offer expires at 5:00 p.m., New York City time, on
                , 2000, unless we extend it.

-  The terms of the new senior notes are substantially identical to those of the
   existing senior notes, except that the new senior notes will not have
   securities law transfer restrictions and registration rights relating to the
   existing senior notes and the new senior notes will not provide for the
   payment of additional interest under circumstances relating to the timing of
   the exchange offer.

-  The exchange offer is not subject to any condition other than that the
   exchange offer not violate applicable law or applicable interpretation of the
   staff of the SEC and certain other conditions.

-  All outstanding senior notes that are validly tendered and not validly
   withdrawn will be exchanged.

-  You may withdraw your tender of existing senior notes any time before the
   exchange offer expires.

-  We will not receive any proceeds from the exchange offer.

-  The exchange of senior notes will not be a taxable event for U.S. federal
   income tax purposes.

   Neither the Securities and Exchange Commission nor any state securities
commission has approved or disapproved of these securities or determined if this
prospectus is truthful or complete. Any representation to the contrary is a
criminal offense.

                             ----------------------

              The date of this prospectus is              , 1999.
<PAGE>   3

<PAGE>   4

                               TABLE OF CONTENTS

<TABLE>
<CAPTION>
                                                                PAGE
                                                                ----
<S>                                                             <C>
Where You Can Find More Information.........................       3
Forward-Looking Statements..................................       4
Prospectus Summary..........................................       5
Use of Proceeds.............................................      13
Capitalization..............................................      13
Business....................................................      14
Management..................................................      17
Description of Outstanding Indebtedness.....................      20
The Exchange Offer..........................................      21
Description of the New Senior Notes.........................      29
United States Federal Income Tax Considerations.............      43
Plan of Distribution........................................      45
Legal Matters...............................................      46
Experts.....................................................      46
</TABLE>

                             ----------------------

                      WHERE YOU CAN FIND MORE INFORMATION

     Alliant Energy Corporation, our parent corporation and the guarantor of the
senior notes, files annual, quarterly and current reports, proxy statements and
other information with the SEC. You may read and copy any document which Alliant
Energy Corporation files at the SEC's public reference rooms at 450 Fifth
Street, N.W., Washington D.C., and at regional SEC offices in Chicago, Illinois
and New York, New York. You can call the SEC at 1-800-SEC-0330 for further
information on the operation of the public reference rooms. You can also find
Alliant Energy Corporation's public filings with the SEC on the internet at a
website maintained by the SEC located at http://www.sec.gov.

     We are "incorporating by reference" specified documents that Alliant Energy
Corporation files with the SEC, which contain important business and financial
information not included in or delivered with this prospectus. "Incorporating by
reference" means:

     -  incorporated documents are considered part of this prospectus;

     -  we are disclosing important information to you by referring you to those
        documents; and

     -  information Alliant Energy Corporation files with the SEC will
        automatically update and supersede information contained in this
        offering memorandum.

     We incorporate by reference the documents we list below and any future
filings Alliant Energy Corporation makes with the SEC under Sections 13(a),
13(c), 14 or 15(d) of the Securities Exchange Act of 1934 after the date of this
prospectus and before the end of the exchange offer:

     -  Alliant Energy Corporation's Annual Report on Form 10-K for the year
        ended December 31, 1998, as amended by Alliant Energy Corporation's Form
        10-K/A filed November 1, 1999;

     -  Alliant Energy Corporation's Reports on Form 10-Q for the quarters ended
        March 31, 1999 and June 30, 1999, each as amended by Alliant Energy
        Corporation's Form 10-Q/As filed on November 1, 1999, and Alliant Energy
        Corporation's Report on Form 10-Q for the quarter ended September 30,
        1999; and

     -  Alliant Energy Corporation's Current Reports on Form 8-K, both dated
        January 20, 1999.

     YOU MAY REQUEST A COPY OF ANY OF THESE FILINGS (INCLUDING EXHIBITS), AT NO
COST, BY WRITING TO EDWARD M. GLEASON, VICE PRESIDENT-TREASURER AND CORPORATE
SECRETARY, ALLIANT ENERGY CORPORATION, 222 WEST WASHINGTON AVENUE, MADISON,
WISCONSIN 53703, OR BY CALLING MR. GLEASON AT (608) 252-3311. TO OBTAIN

                                        3
<PAGE>   5

TIMELY DELIVERY OF ANY OF THIS INFORMATION, YOU MUST MAKE YOUR REQUEST AT LEAST
FIVE BUSINESS DAYS PRIOR TO THE EXPIRATION OF THE EXCHANGE OFFER. THE DATE BY
WHICH YOU MUST MAKE YOUR REQUEST IS           , 2000.

     You should rely only on the information contained or incorporated by
reference in this document or to which we have referred you. We have not
authorized any other person to provide you with different information. This
prospectus may only be used where it is legal to sell these securities. You
should assume that the information contained or incorporated by reference in
this document is accurate as of the date on the front cover of the prospectus
only. Our and Alliant Energy Corporation's business, financial condition,
results of operations and prospects may have changed since that date.

                           FORWARD-LOOKING STATEMENTS

     This prospectus (including the information we incorporate by reference)
contains forward-looking statements that are not of historical fact and are
statements intended to qualify for the safe harbors from liability established
by the Private Securities Litigation Reform Act of 1995. From time to time, we
or Alliant Energy Corporation may make other forward-looking statements within
the meaning of the federal securities laws that involve judgments, assumptions
and other uncertainties beyond our control. These forward-looking statements may
include, among others, statements concerning revenue and cost trends, cost
recovery, cost reduction strategies and anticipated outcomes, pricing
strategies, changes in the utility industry, planned capital expenditures,
financing needs and availability, statements of expectations, beliefs, future
plans and strategies, anticipated events or trends and similar comments
concerning matters that are not historical facts. You are cautioned that these
statements are not a guarantee of future performance and that these
forward-looking statements are subject to risks and uncertainties that could
cause actual results to differ materially from those expressed in, or implied
by, these statements. Some, but not all, of the risks and uncertainties include:

     -  weather effects on sales and revenues,

     -  competitive factors,

     -  general economic conditions in the relevant service territory,

     -  federal and state regulatory or government actions, including the
        deregulation of the utility industry,

     -  unanticipated construction and acquisition expenditures,

     -  issues related to stranded costs and their recovery,

     -  the operations of Alliant Energy Corporation's nuclear facilities,

     -  unanticipated issues or costs associated with achieving Year 2000
        compliance,

     -  unanticipated costs associated with certain environmental remediation
        efforts being undertaken by Alliant Energy Corporation,

     -  material changes in the value of our investment in McLeodUSA
        Incorporated,

     -  technological developments,

     -  employee workforce factors, including changes in key executives,
        collective bargaining agreements or work stoppages,

     -  political, legal and economic conditions in foreign countries Alliant
        Energy Corporation has investments in, and

     -  changes in the rate of inflation.

                             ----------------------

     In this prospectus, "we," "us" and "our" refer to Alliant Energy Resources,
Inc.

                                        4
<PAGE>   6

                               PROSPECTUS SUMMARY

     The following summary highlights selected information from this prospectus
and may not contain all of the information that is important to you. This
prospectus includes the specific terms of the new senior notes we are offering,
as well as information regarding our business. We encourage you to read this
prospectus in its entirety.

                         ALLIANT ENERGY RESOURCES, INC.

OVERVIEW

     We are a wholly-owned subsidiary of Alliant Energy Corporation, which is a
registered public utility holding company. We manage a portfolio of companies
involved in non-regulated businesses. These businesses include providing energy
and environmental services, energy generation and infrastructure in growing
domestic and international markets, products and services to meet the needs of
residential and small commercial customers, electricity marketing and risk
management services to wholesale customers, transportation services, and
financing for affordable housing developments. Our primary subsidiaries include
Alliant Energy Investments, Inc.; Alliant Energy International, Inc.; and
Alliant Energy Industrial Services, Inc. Alliant Energy Corporation also has a
50% ownership interest in a joint venture with Cargill Incorporated, named
Cargill-Alliant LLC.

     Set forth below is a condensed organization chart that reflects how our and
Alliant Energy Corporation's businesses and investments are managed:

                                  [FLOW CHART]

     Our principal executive offices are located at Alliant Tower, 200 First
Street SE, Cedar Rapids, Iowa 52401, telephone number (319) 398-4411.

STRATEGY

     As competitive forces shape the energy-services industry, energy providers
are being challenged to increase growth and profits. Because we expect
consumption of electricity and natural gas to grow only modestly within Alliant
Energy Corporation's domestic utility service territory, we have entered several
energy-services markets that we expect will provide opportunities for new
sources of growth. We have

                                        5
<PAGE>   7

established new distinct platforms to complement our existing non-regulated
investments, which are designed to meet customer needs. These platforms and
existing investments include:

     - Investments: Our existing investments include an oil and gas production
       company, a short-line railroad, a barge company, an affordable housing
       company, various real estate joint ventures and an equity stake in an
       independent telecommunications provider.

     - International: We are a partner in developing, or are seeking to develop,
       energy generation and infrastructure in New Zealand, Australia, China,
       Mexico and Brazil, markets which we have selected because of their growth
       potential.

     - Industrial Services: We are a provider of energy and environmental
       services designed to maximize productivity for industrial and large
       commercial customers.

     - Cargill-Alliant: Alliant Energy Corporation has an energy-trading joint
       venture with Cargill Incorporated, one of the world's largest and most
       established commodity trading firms, that combines the risk-management
       and commodity trading expertise of Cargill with Alliant Energy
       Corporation's low-cost electricity generation and transmission business
       experience.

     - Mass Markets: We are a provider of a growing array of products and
       services designed to meet the comfort, security and productivity needs of
       residential and small commercial customers.

                           ALLIANT ENERGY CORPORATION

     Alliant Energy Corporation was formed as a result of a three-way merger
involving WPL Holdings, Inc., IES Industries Inc. and Interstate Power Company.
The merger was completed in April 1998. The first tier subsidiaries of Alliant
Energy Corporation include Wisconsin Power and Light Company, IES Utilities
Inc., Interstate Power Company, Alliant Energy Resources, Inc. and Alliant
Energy Corporate Services, Inc.

     Alliant Energy Corporation, through its public utility operating companies,
Wisconsin Power and Light Company, IES Utilities Inc. and Interstate Power
Company, is engaged principally in:

     -  the generation, transmission, distribution and sale of electric energy;

     -  the purchase, distribution, transportation and sale of natural gas; and

     -  the provision of water and steam services in selected markets.

The principal markets of Alliant Energy Corporation's utility operating
subsidiaries are located in Iowa, Wisconsin, Minnesota and Illinois. Alliant
Energy Corporation is also involved in several non-regulated and non-utility
activities through our company.

     Alliant Energy Corporation, a public utility holding company incorporated
in Wisconsin in 1981, has its principal executive offices located at 222 West
Washington Avenue, Madison, Wisconsin 53703, telephone number (608) 252-3311.

                               THE EXCHANGE OFFER

Existing Senior Notes......  We sold $250,000,000 of our 7 3/8% Senior Notes due
                             2009, which are unconditionally guaranteed by
                             Alliant Energy Corporation, to the initial
                             purchasers on November 9, 1999. The initial
                             purchasers resold those senior notes (the "existing
                             senior notes") to qualified institutional buyers
                             pursuant to Rule 144A under the Securities Act of
                             1933.

Registration Rights
Agreement..................  When we sold the existing senior notes we entered
                             into a registration rights agreement with the
                             initial purchasers in which we agreed, among other
                             things, to provide to you and all other holders of
                             these existing senior notes the opportunity to
                             exchange your unregistered
                                        6
<PAGE>   8

                             existing senior notes for a new series of
                             substantially identical new senior notes that we
                             have registered under the Securities Act. This
                             exchange offer is being made for that purpose.

New Senior Notes...........  We are offering registered 7 3/8% Senior Notes due
                             2009, which are unconditionally guaranteed by
                             Alliant Energy Corporation (the "new senior
                             notes"), in exchange for your existing senior
                             notes. The terms of the new senior notes and the
                             existing senior notes are substantially identical
                             except:

                             -  the new senior notes will be issued in a
                                transaction that will have been registered under
                                the Securities Act;

                             -  the new senior notes will not contain securities
                                law restrictions on transfer; and

                             -  the new senior notes will not provide for the
                                payment of additional interest under
                                circumstances relating to the timing of the
                                exchange offer.

The Exchange Offer.........  We are offering to exchange $1,000 principal amount
                             of the new senior notes for each $1,000 principal
                             amount of your existing senior notes. As of the
                             date of this prospectus, $250,000,000 aggregate
                             principal amount of the existing senior notes are
                             outstanding. For procedures for tendering, see "The
                             Exchange Offer -- Procedures for Tendering Existing
                             Senior Notes"

Expiration Date............  This exchange offer will expire at 5:00 p.m., New
                             York City time, on             , 2000, unless we
                             extend it.

Resales of New Senior
Notes......................  We believe that you may resell or otherwise
                             transfer the new senior notes received in the
                             exchange offer without complying with the
                             registration and prospectus delivery provisions of
                             the Securities Act so long as you are not a
                             broker-dealer and you meet the following
                             conditions:

                             -  you are not our "affiliate" within the meaning
                                of Rule 405 under the Securities Act;

                             -  you acquire the new senior notes issued in the
                                exchange offer in the ordinary course of your
                                business; and

                             -  you have no arrangement or understanding with
                                any person to participate in the distribution of
                                the new senior notes.

                             By signing the letter of transmittal and tendering
                             your existing senior notes, you will be making
                             representations to this effect. You may incur
                             liability under the Securities Act if:

                             -  any of the representations listed above are not
                                true; and

                             -  you transfer any new senior note issued to you
                                in the exchange offer without either delivering
                                a prospectus meeting the requirements of the
                                Securities Act or qualifying for an exemption
                                from the registration requirements under the
                                Securities Act.

                             We do not assume or indemnify you against liability
                             under these circumstances, which means that we will
                             not protect you against any loss incurred as a
                             result of this liability under the Securities Act.

                                        7
<PAGE>   9

                             Each broker-dealer that has received new senior
                             notes for its own account in exchange for existing
                             senior notes that were acquired as a result of
                             market-making or other trading activities must
                             acknowledge that it will deliver a prospectus
                             meeting the requirements of the Securities Act in
                             connection with any resale of the new senior notes.
                             A broker-dealer generally may use this prospectus
                             in connection with any such resale. See "The
                             Exchange Offer -- Resales of New Senior Notes."

Acceptance of Existing
Senior Notes and Delivery
  of New Senior Notes......  We will accept for exchange any and all existing
                             senior notes that are validly tendered in the
                             exchange offer and not withdrawn before the offer
                             expires. The new senior notes will be delivered
                             promptly following the exchange offer.

Withdrawal Rights..........  You may withdraw your tender of existing senior
                             notes at any time before the exchange offer
                             expires.

Conditions of the Exchange
Offer......................  The exchange offer is subject to certain
                             conditions, which we may waive.

Consequences of Failure to
  Exchange.................  If you are eligible to participate in the exchange
                             offer and you do not tender your existing senior
                             notes, then you will not have further exchange or
                             registration rights and you will continue to hold
                             existing senior notes subject to restrictions on
                             transfer.

Federal Income Tax
  Consequences.............  The exchange of an existing senior note for a new
                             senior note will not be taxable to a United States
                             holder for federal income tax purposes.
                             Consequently, you will not recognize any gain or
                             loss upon receipt of the new senior notes. See
                             "United States Federal Income Tax Consequences."

Use of Proceeds............  We will not receive any proceeds from the exchange
                             offer.

Accounting Treatment.......  We will not recognize any gain or loss on the
                             exchange of senior notes. See "The Exchange
                             Offer -- Accounting Treatment."

Exchange Agent.............  Firstar Bank, N.A. is the exchange agent. See "The
                             Exchange Offer -- Exchange Agent."

                              THE NEW SENIOR NOTES

     The new senior notes will evidence the same debt as the existing senior
notes and will be governed by the same indenture, as supplemented, under which
the existing senior notes were issued.

TERMS OF THE NEW SENIOR NOTES

Aggregate Principal
Amount.....................  Up to $250,000,000.

Interest Rate..............  7 3/8% per year.

Maturity Date..............  November 9, 2009.

Interest Payment Dates.....  May 9 and November 9 of each year, beginning May 9,
                             2000.

                                        8
<PAGE>   10

Interest Calculations......  Based on a 360-day year of twelve 30-day months.

Parent Company Guarantee...  Our parent, Alliant Energy Corporation, will
                             unconditionally guarantee the new senior notes. The
                             guarantee will be equal in right of payment with
                             all other unsecured indebtedness and guarantees
                             issued by our parent.

Ranking....................  The new senior notes will rank equally with all of
                             our other unsecured and unsubordinated
                             indebtedness.

Optional Redemption........  The new senior notes will be redeemable in whole or
                             in part at our option at any time, on at least 30
                             days' but not more than 60 days' prior written
                             notice at a price equal to the greater of (a) 100%
                             of the principal amount of the new senior notes
                             being redeemed and (b) the sum of the present
                             values of the principal amount of the new senior
                             notes to be redeemed and the remaining scheduled
                             payments of interest on the new senior notes from
                             the redemption date to November 9, 2009, discounted
                             from their respective scheduled payment dates to
                             the redemption date semi-annually (assuming a
                             360-day year consisting of twelve 30-day months) at
                             a discount rate equal to the Treasury Yield (as
                             defined under "Description of the New Senior
                             Notes -- Optional Redemption") plus 20 basis
                             points, plus accrued interest on the senior notes
                             to the redemption date. See "Description of the New
                             Senior Notes -- Optional Redemption."

Sinking Fund...............  None.

Form and Denominations.....  The new senior notes initially will be issued in
                             fully registered book-entry form and will be
                             represented by one or more registered global
                             securities deposited with or on behalf of, and
                             registered in the name of, a nominee of The
                             Depository Trust Company. The new senior notes will
                             be issued in denominations of $1,000 and integral
                             multiples thereof.

Absence of Market for the
Notes......................  The new senior notes are a new issue of securities
                             with no established trading market. We currently
                             have no intention to apply to list the new senior
                             notes on any securities exchange or to seek their
                             admission to trading on any automated quotation
                             system. Accordingly, there can be no assurance as
                             to the development or liquidity of any market for
                             the new senior notes.

GENERAL INDENTURE PROVISIONS APPLICABLE TO THE NEW SENIOR NOTES

No Limit on Debt...........  The indenture governing the new senior notes does
                             not limit the amount of debt that we may issue or
                             provide holders any protection should we be
                             involved in a highly leveraged transaction.

Certain Covenants..........  The indenture contains covenants that, among other
                             things, will limit our ability and that of our
                             subsidiaries and, for some limited matters, Alliant
                             Energy Corporation to:

                             -  issue, assume or guarantee certain additional
                                secured indebtedness;

                             -  engage in sale and lease-back transactions; and

                             -  consolidate or merge.

                                        9
<PAGE>   11

                             These covenants are subject to important exceptions
                             and qualifications, which are described under the
                             heading "Description of the New Senior
                             Notes -- Covenants" in this prospectus.

Events of Default..........  Each of the following is an event of default under
                             the indenture:

                             -  the failure by us or Alliant Energy Corporation
                                to pay principal of or premium, if any, on the
                                senior notes when due;

                             -  the failure by us or Alliant Energy Corporation
                                for 30 days to pay interest when due on the
                                senior notes;

                             -  the failure by us or Alliant Energy Corporation
                                to perform other covenants with respect to the
                                senior notes following 90 days after receipt of
                                notice of failure; and

                             -  certain events of bankruptcy, insolvency or
                                reorganization of us or Alliant Energy
                                Corporation.

                             These covenants are subject to important exceptions
                             and qualifications, which are described under the
                             heading "Description of the New Senior
                             Notes -- Events of Default" in this prospectus.

Remedies...................  If any event of default occurs and is continuing,
                             the trustee under the indenture or holders of at
                             least 25% in aggregate principal amount of
                             outstanding senior notes may declare the principal
                             thereof immediately due and payable.

Other......................  The new senior notes and the existing senior notes
                             will vote together as a single class for purposes
                             of determining whether the holders of the requisite
                             percentage in outstanding principal amount have
                             taken certain actions or exercised certain rights
                             under the indenture.

                                       10
<PAGE>   12

                         SUMMARY FINANCIAL INFORMATION

ALLIANT ENERGY RESOURCES, INC.

     The following table sets forth our unaudited summary consolidated financial
information. The information set forth below was derived from Alliant Energy
Corporation's financial statements and notes. The unaudited interim period
financial information, in our opinion, includes all adjustments, which are
normal and recurring in nature, necessary for a fair presentation for the
periods shown. Results for the nine months ended September 30, 1999 are not
necessarily indicative of results to be expected for the full fiscal year.

<TABLE>
<CAPTION>
                                               NINE MONTHS ENDED
                                                 SEPTEMBER 30,            YEAR ENDED DECEMBER 31,
                                              --------------------    --------------------------------
                                                1999        1998        1998        1997        1996
                                              --------    --------    --------    --------    --------
                                                                   (IN THOUSANDS)
<S>                                           <C>         <C>         <C>         <C>         <C>
INCOME STATEMENT DATA:
Operating revenues........................    $202,863    $177,269    $238,676    $361,961    $393,963
Operating income (loss)...................         296      (5,533)     (8,608)     (6,818)     (6,666)
Income (loss) from continuing operations
  before discontinued operations..........      27,013(1)   (8,142)     (8,898)     (3,966)     (1,851)
Net income (loss).........................      27,013(1)   (8,142)     (8,898)     (3,966)     (3,148)
</TABLE>

<TABLE>
<CAPTION>
                                                           SEPTEMBER 30,             DECEMBER 31,
                                                       ----------------------    --------------------
                                                          1999         1998        1998        1997
                                                       ----------    --------    --------    --------
                                                                       (IN THOUSANDS)
<S>                                                    <C>           <C>         <C>         <C>
BALANCE SHEET DATA:
Current assets.....................................    $  104,745    $ 87,994    $ 92,148    $ 92,703
Non-current assets(2)..............................     1,381,858     662,116     777,113     745,801
Current liabilities................................        52,605      53,402      63,648     101,399
Non-current liabilities (excludes minority
  interest)........................................       370,508     108,372     160,278     153,872
Minority interest(3)...............................         7,138       6,633       6,193       5,446
</TABLE>

---------------
(1) Includes after-tax gains of $21 million from the sale of a portion of our
    investment in McLeodUSA Incorporated.

(2) Includes the market value of McLeodUSA Incorporated of $818 million at
    September 30, 1999, $223 million at September 30, 1998, $320 million at
    December 31, 1998 and $328 million at December 31, 1997.

(3) Minority interest represents primarily real estate joint ventures.

                                       11
<PAGE>   13

ALLIANT ENERGY CORPORATION

     The following table sets forth selected consolidated financial information
of Alliant Energy Corporation. The information set forth below was selected or
derived from the financial statements and notes of Alliant Energy Corporation.
The unaudited interim period financial information, in the opinion of Alliant
Energy Corporation, includes all adjustments, which are normal and recurring in
nature, necessary for a fair presentation for the periods shown. Results for the
nine months ended September 30, 1999 are not necessarily indicative of results
to be expected for the full fiscal year. The information set forth below is
qualified in its entirety by and should be read in conjunction with the Alliant
Energy Corporation Management's Discussion and Analysis of Financial Condition
and Results of Operations and the detailed information and consolidated
financial statements, including the notes thereto, incorporated by reference in
this prospectus. See "Where You Can Find More Information."

<TABLE>
<CAPTION>
                           NINE MONTHS ENDED
                             SEPTEMBER 30,                           YEAR ENDED DECEMBER 31,
                        -----------------------   --------------------------------------------------------------
                           1999         1998       1998(1)        1997         1996         1995         1994
                        ----------   ----------   ----------   ----------   ----------   ----------   ----------
                                            (DOLLARS IN THOUSANDS EXCEPT FOR PER SHARE DATA)
<S>                     <C>          <C>          <C>          <C>          <C>          <C>          <C>
INCOME STATEMENT DATA:
Operating revenues....  $1,631,305   $1,602,608   $2,130,874   $2,300,627   $2,232,840   $1,976,807   $1,889,231
Operating income......     284,046      228,704      283,302      336,383      365,439      364,932      313,508
Income from continuing
  operations..........     151,784       71,481       96,675      144,578      157,088      159,157      147,064
Net income............     151,784       71,481       96,675      144,578      155,791      145,971      145,890
PER SHARE DATA:
Income from continuing
  operations..........       $1.94        $0.93        $1.26        $1.90        $2.08        $2.13        $1.99
Earnings per average
  common share (basic
  and diluted)........       $1.94        $0.93        $1.26        $1.90        $2.06        $1.95        $1.98
Dividends declared per
  common share(2).....       $1.50        $1.50        $2.00        $2.00        $1.97        $1.94        $1.92
BALANCE SHEET DATA:
Total assets..........  $5,597,245   $4,710,128   $4,959,337   $4,923,550   $4,639,826   $4,476,406   $4,269,637
Long-term obligations,
  net.................  $1,744,687   $1,664,665   $1,713,649   $1,604,305   $1,444,355   $1,357,755   $1,358,258
RATIO OF EARNINGS TO
  FIXED CHARGES.......        3.34         2.28         2.17         2.77         3.21         3.17         3.17
</TABLE>

---------------

(1) The 1998 financial results reflect the recording of $54 million of pre-tax
    merger charges.

(2) Represents data for WPL Holdings, Inc. prior to the three-way merger
    involving WPL Holdings, Inc., IES Industries Inc. and Interstate Power
    Company in April 1998.

                                       12
<PAGE>   14

                                USE OF PROCEEDS

     This exchange offer is intended to satisfy our obligations under the
registration rights agreement entered into in connection with the issuance of
the existing senior notes. We will not receive any cash proceeds from the
issuance of the new senior notes.

     The net proceeds from the sale of the existing senior notes were
approximately $247 million. We added the net proceeds from the sale of the
existing senior notes to our general funds. We expect to use our general funds
to repay commercial paper we issued in connection with the development and
acquisition of non-regulated businesses as it becomes due. To the extent we do
not use the net proceeds for repayment of commercial paper, we may also use the
net proceeds to fund our existing operations, including potential acquisitions.
We invested general funds not immediately used for these purposes or other
purposes in short-term instruments. At September 30, 1999, we had $329.5 million
of commercial paper outstanding and backed by our 3-Year Credit Agreement, with
a weighted-average maturity of 24.3 days and a weighted-average interest rate of
5.54%.

                                 CAPITALIZATION

     The following table sets forth the consolidated capitalization of Alliant
Energy Corporation (including us) as of September 30, 1999, and as adjusted to
give effect to the sale of the existing senior notes.

<TABLE>
<CAPTION>
                                                                   SEPTEMBER 30, 1999
                                                                ------------------------
                                                                  ACTUAL       ADJUSTED
                                                                ----------    ----------
                                                                     (IN THOUSANDS)
<S>                                                             <C>           <C>
Common stock................................................    $      787    $      787
Additional paid-in capital..................................       934,373       934,373
Retained earnings...........................................       572,035       572,035
Accumulated other comprehensive income......................       475,625       475,625
                                                                ----------    ----------
  Total common equity.......................................     1,982,820     1,982,820
                                                                ----------    ----------
Cumulative preferred stock of subsidiaries..................       113,604       113,604
Long-term debt (excluding current portion)..................     1,569,531     1,819,531
                                                                ----------    ----------
  Total capitalization......................................    $3,665,955    $3,915,955
                                                                ==========    ==========
</TABLE>

                                       13
<PAGE>   15

                                    BUSINESS

OVERVIEW

     We are a wholly-owned subsidiary of Alliant Energy Corporation, which is a
registered public utility holding company. We manage a portfolio of companies
involved in non-regulated businesses. These businesses include providing energy
and environmental services, energy generation and infrastructure in growing
domestic and international markets, products and services to meet the needs of
residential and small commercial customers, electricity marketing and risk
management services to wholesale customers, transportation services, and
financing for affordable housing developments. Our primary subsidiaries include
Alliant Energy Investments, Inc.; Alliant Energy International, Inc.; and
Alliant Energy Industrial Services, Inc. Alliant Energy Corporation also has a
50% ownership interest in a joint venture with Cargill Incorporated, named
Cargill-Alliant LLC.

     We were incorporated in Wisconsin in 1988 as Heartland Development
Corporation, a subsidiary of WPL Holdings, Inc. As part of a three-way merger
involving our parent in April 1998, we merged with IES Diversified Inc., the
holding company for the non-regulated businesses of the former IES Industries
Inc., to form Alliant Energy Resources, Inc. Our principal executive offices are
located at Alliant Tower, 200 First Street SE, Cedar Rapids, Iowa 52401,
telephone number (319) 398-4411.

STRATEGY

     As competitive forces shape the energy-services industry, energy providers
are being challenged to increase growth and profits. Because we expect
consumption of electricity and natural gas to grow only modestly within Alliant
Energy Corporation's domestic utility service territory, we have entered several
energy-services markets that we expect will provide opportunities for new
sources of growth. We have established new distinct platforms to complement our
existing non-regulated investments, which are designed to meet customer needs.
These platforms and existing investments include:

     -  Investments:  Our existing investments include an oil and gas production
        company, a short-line railroad, a barge company, an affordable housing
        company, various real estate joint ventures and an equity stake in an
        independent telecommunications provider.

     -  International:  We are a partner in developing, or are seeking to
        develop, energy generation and infrastructure in New Zealand, Australia,
        China, Mexico and Brazil, markets which we have selected because of
        their growth potential. We continued our expansion in 1998 by making a
        strategic investment in Peak Pacific Investment Company PTE Ltd., an
        energy development firm based in Singapore and active in China. Peak
        Pacific broke ground on a new power plant in 1999 near Zhengding. We are
        similarly seeking to expand our New Zealand presence and have recently
        entered the Australian energy market. We are also seeking opportunities
        in the South American energy marketplace.

     -  Industrial Services:  We are a provider of energy and environmental
        services designed to maximize productivity for industrial and large
        commercial customers. We created Alliant Energy Industrial Services in
        1998 by combining two new units -- Energy Planning and Energy Management
        -- with two established businesses: Energy Applications, which provides
        facilities-based and commodities-based energy solutions; and RMT, Inc.,
        an environmental-management and engineering firm with offices throughout
        the United States and the United Kingdom. We believe these four
        components comprise an industrial services company with expertise that
        customers find valuable.

     -  Cargill-Alliant:  Alliant Energy Corporation has an energy-trading joint
        venture with Cargill Incorporated, one of the world's largest and most
        established commodity trading firms, that combines the risk-management
        and commodity trading expertise of Cargill with Alliant Energy
        Corporation's low-cost electricity generation and transmission business
        experience. Cargill-Alliant LLC officially began operations in 1997 and
        has an initial term through October 2002.

                                       14
<PAGE>   16

     -  Mass Markets:  We are a provider of a growing array of products and
        services designed to meet the comfort, security and productivity needs
        of residential and small commercial customers. We continue to pursue
        opportunities in a growing residential and small commercial marketplace.

PRINCIPAL OPERATIONS

     We conduct our operations through our principal subsidiaries and
investments, which are engaged in the businesses described below:

     Investments:  Our subsidiaries and investments include Whiting Petroleum
Corporation, Alliant Energy Transportation, Inc. and Alliant Energy Investments,
Inc., which is a holding company whose primary subsidiaries include Heartland
Properties, Inc. and Capital Square Financial Corporation and which holds an
equity stake in McLeodUSA Incorporated. Alliant Energy Investments also has
direct and indirect equity interests in various real estate and economic
development ventures, primarily concentrated in Iowa.

     -  Whiting Petroleum is based in Denver, Colorado and was organized to
        purchase, develop and produce crude oil and natural gas. Whiting
        Petroleum's construction and acquisition expenditures were approximately
        $60 million in 1998 and are anticipated to be approximately $35 million
        in 1999.

     -  Alliant Energy Transportation is a holding company whose equity
        investments total $20 million as of September 30, 1999 and include the
        Cedar Rapids and Iowa City Railway Company, a short-line railway, which
        renders freight service between Cedar Rapids and Iowa City, Transfer
        Services, Inc., which provides transloading and storage services, and a
        75% equity investment in IEI Barge Services Inc., which provides barge
        terminal and hauling services on the Mississippi River.

     -  Heartland Properties, formed in 1988, is responsible for performing
        asset management and facilitating the development and financing of high
        quality, affordable housing in Wisconsin and the Midwest. Heartland
        Properties has a majority ownership interest in 60 properties.

     -  Capital Square was incorporated in 1992 to provide mortgage banking
        services to facilitate Heartland Properties' development and financing
        efforts in the affordable housing market.

     -  We also hold an equity interest of approximately 11% in McLeodUSA
        Incorporated. McLeodUSA is an independent telecommunications provider
        based in Cedar Rapids, Iowa. Our investment in McLeodUSA had a market
        value of approximately $818 million as of September 30, 1999 (based on a
        closing price of $42.5625 per share and compared to a cost basis of
        approximately $30 million). Alliant Energy Investments is a party to a
        stockholders' agreement that provides, subject to certain exceptions,
        that it may not sell any equity securities of McLeodUSA until December
        31, 2001 without the consent of the Board of Directors of McLeodUSA.

     International:  Our international operations include Alliant Energy
International, Inc., a holding company whose primary investments include Alliant
International New Zealand Limited, Alliant Energy Australia Pty Ltd., Interstate
Energy Corporation Pte. Ltd., Grandelight Holdings Ltd., Alliant Energy de
Mexico L.L.C. and Alliant Energy Brazil, Inc.

     -  Alliant International New Zealand has made equity investments in several
        New Zealand utility entities since 1995, which totaled $111 million as
        of September 30, 1999. As a result of electricity reforms since 1995,
        several utility companies exited generation and retail businesses. As
        part of its strategy to enter the generation and retail markets, Alliant
        International New Zealand sold all of its interest in Central Power
        Limited and a portion of its interest in Powerco Limited, each of which
        were electricity distribution companies. Alliant International New
        Zealand has a 10% interest in Infrastructure and Utilities NZ Ltd
        ("Infratil NZ"), a holding company for infrastructure and utility
        businesses in New Zealand. Together with Infratil NZ, Alliant
        International New Zealand intends to increase its interest in
        TrustPower, an electricity generation and retail company, from the
        current level of 41%.

                                       15
<PAGE>   17

     -  In October 1999, Alliant Energy Australia acquired a 10% equity interest
        in Infratil Australia Limited, a holding company for infrastructure and
        utility businesses in Australia. Alliant Energy Australia expects to
        close on the acquisition of a 22% equity interest in Southern Hydro, a
        hydro-electricity generation business, in late December 1999.

     -  As of September 30, 1999, Alliant Energy International has invested $61
        million in investments in China, which consist of an equity investment
        of $26 million in two individual cogeneration facilities in China and an
        equity investment of $35 million in Peak Pacific Investment Company PTE
        Ltd. Peak Pacific was formed to develop investment opportunities in
        generation infrastructure projects in China. In addition, we have
        commitments of an additional $12 million to invest in China as of
        September 30, 1999.

     -  Alliant Energy de Mexico owns two subsidiaries incorporated in Mexico
        that have entered into agreements to operate the electrical distribution
        facilities serving a resort community known as Laguna del Mar, located
        in Puerto Penasco, Sonora, Mexico. As of September 30, 1999, Alliant
        Energy International's investment consisted of $9 million in secured
        debentures of Laguna del Mar.

     -  Alliant Energy Brazil was formed for the purposes of making investments
        in Brazil. Several opportunities have arisen as a result of the
        Brazilian government's privatization of the electricity sector. Alliant
        Energy Brazil continues to examine opportunities in electricity
        generation and distribution arising as a result of the privatization.

     Industrial Services:  Our industrial services include Alliant Energy
Industrial Services, Inc., a holding company whose primary wholly-owned
subsidiaries include Industrial Energy Applications, Inc. and RMT, Inc.

     -  Industrial Energy Applications offers to its customers commodities-based
        energy services, such as supplying natural gas and electricity, and
        facilities-based energy services, including standby generation,
        cogeneration, steam production and propane air systems. It also provides
        energy consulting services for customers and owns two oil and natural
        gas gathering systems in Texas.

     -  RMT is a Madison, Wisconsin-based environmental and engineering
        consulting company that serves clients nationwide in a variety of
        industrial market segments. The most significant of these markets are
        chemical companies, pulp and paper processors, oil and gas providers,
        foundries and other manufacturers. RMT specializes in consulting on
        solid and hazardous waste management, ground water quality protection,
        industrial design and hygiene engineering, and air and water pollution
        control.

                                       16
<PAGE>   18

                                   MANAGEMENT

     The following table sets forth information as of September 30, 1999,
concerning our executive officers and directors. Except as otherwise indicated,
each executive officer and director has been engaged in his or her present
office or occupation for at least the past five years.

<TABLE>
<CAPTION>
NAME                                        AGE                          TITLE
----                                        ---                          -----
<S>                                         <C>    <C>
Erroll B. Davis, Jr.......................  55     Chief Executive Officer and Director
James E. Hoffman..........................  46     President
Thomas L. Aller...........................  50     Vice President -- Alliant Energy Investments
Charles Castine...........................  50     Vice President -- Industrial Services
John K. Peterson..........................  47     Vice President -- International
John E. Ebright...........................  56     Vice President -- Controller
Edward M. Gleason.........................  59     Vice President -- Treasurer and Corporate
                                                   Secretary
Linda J. Wentzel..........................  51     Assistant Corporate Secretary
Enrique Bacalao...........................  50     Assistant Treasurer
Steven F. Price...........................  47     Assistant Treasurer
Robert A. Rusch...........................  37     Assistant Treasurer
Daniel L. Siegfried.......................  39     Assistant Corporate Secretary
Alan B. Arends............................  66     Director
Rockne G. Flowers.........................  68     Director
Joyce L. Hanes............................  67     Director
Lee Liu...................................  66     Director
Katherine C. Lyall........................  58     Director
Arnold M. Nemirow.........................  56     Director
Milton E. Neshek..........................  69     Director
Jack R. Newman............................  66     Director
Judith D. Pyle............................  56     Director
Robert D. Ray.............................  71     Director
Robert W. Schlutz.........................  64     Director
Wayne H. Stoppelmoor......................  65     Director
Anthony R. Weiler.........................  63     Director
</TABLE>

     Erroll B. Davis, Jr. has served as Chief Executive Officer since 1990 and
has been a director since 1988. Mr. Davis also has served as President and Chief
Executive Officer of Alliant Energy Corporation since 1990.

     James E. Hoffman was elected President in April 1998. Mr. Hoffman also was
elected Executive Vice President-Business Development of Alliant Energy
Corporation effective April 1998. Previously, he served as Executive Vice
President since 1996 at IES Utilities Inc. and Executive Vice President-Customer
Service & Energy Delivery from 1995 to 1997 at IES Utilities Inc. Prior to that
time, he was Chief Information Officer from 1990 to 1995 at MCI Communications.

     Thomas L. Aller was elected Vice President-Alliant Energy Investments in
1998. From 1993 to 1998, Mr. Aller served as Vice President-Real Estate, IES
Investments, Inc. Prior to that time, he served as Executive Vice President,
2001 Development Corporation beginning in 1988, and was Executive Assistant to
the Mayor and City Council of Cedar Rapids from 1972 to 1988.

     Charles Castine was elected Vice President-Industrial Services in 1998.
From 1994 to 1998, Mr. Castine served as Vice President, Consumer Service
Division, GE Appliance Business. Prior to that time, he served with General
Electric Power Generation in various capacities.

     John K. Peterson was elected Vice President-International effective July
1998. From 1994 to 1998, Mr. Peterson served as Vice President, Latin America,
Pacific Enterprises International and, from 1993 to

                                       17
<PAGE>   19

1994, he served as Manager, Corporate and Strategic Planning at the same firm.
Prior to that, he served in a number of management assignments with Southern
California Gas Company.

     John E. Ebright was elected Vice President-Controller effective April 1998.
From 1996 to 1998, Mr. Ebright served as Controller and Chief Accounting Officer
at IES Industries Inc. and IES Utilities Inc. Prior to that time, he was Vice
President and Controller from 1987 to 1996 at MidCon Corp., a subsidiary of
Occidental Petroleum Corporation. Mr. Ebright is also an officer of Alliant
Energy Corporation, IES Utilities Inc. and Wisconsin Power and Light Company.

     Edward M. Gleason was elected Vice President-Treasurer and Corporate
Secretary in 1993. Mr. Gleason has served as Vice President-Treasurer and
Corporate Secretary of Alliant Energy Corporation since 1993. He also has served
as Treasurer and Corporate Secretary of Wisconsin Power and Light Company since
1996 and Corporate Secretary of Wisconsin Power and Light Company from 1993 to
1996.

     Linda J. Wentzel was appointed Assistant Corporate Secretary effective May
1998. Ms. Wentzel has served as Assistant Corporate Secretary of Alliant Energy
Corporation since May 1998. From 1995 to 1998, Ms. Wentzel served as Executive
Administrative Assistant and, from 1992 to 1995, she served as Administrative
Assistant at Alliant Energy Corporation. Ms. Wentzel is also an officer of IES
Utilities Inc. and Wisconsin Power and Light Company.

     Enrique Bacalao was appointed Assistant Treasurer effective November 1998.
From 1995 to 1998, Mr. Bacalao was Vice President, Corporate Banking at the
Chicago Branch, and, from 1993 to 1995, he served as Manager and Head of the
Customer Dealing Group at the London Branch of The Industrial Bank of Japan,
Limited. Mr. Bacalao is also an officer of Alliant Energy Corporation, IES
Utilities Inc. and Wisconsin Power and Light Company.

     Steven F. Price was elected Assistant Treasurer effective April 1998. Prior
to that time, Mr. Price served as Assistant Corporate Secretary of Alliant
Energy Corporation and Wisconsin Power and Light Company and Assistant Treasurer
of Alliant Energy Corporation. Mr. Price is also an officer of IES Utilities
Inc. and Wisconsin Power and Light Company.

     Robert A. Rusch was elected Assistant Treasurer effective April 1998. Prior
to that time, Mr. Rusch served as Assistant Treasurer of Wisconsin Power and
Light Company from 1995 and Financial Analyst from 1989 to 1995 at Wisconsin
Power and Light Company. Mr. Rusch is also an officer of IES Utilities Inc. and
Wisconsin Power and Light Company.

     Daniel L. Siegfried was elected Assistant Corporate Secretary effective
April 1998. Mr. Siegfried also serves as Senior Attorney for Alliant Energy
Corporation. From 1992 to 1998, he served as Senior Environmental Counsel at IES
Industries Inc.

     Alan B. Arends has served as a director since April 1998. Mr. Arends
founded Alliance Benefit Group Financial Services Corp., an employee benefits
company, in 1983 and is currently its Chairman.

     Rockne G. Flowers has served as a director since 1988. Mr. Flowers is
Chairman of Nelson Industries, Inc., a muffler, filter, industrial silencer and
active sound and vibration control technology and manufacturing firm.

     Joyce L. Hanes has served as a director since April 1998. Ms. Hanes has
been the Chairman of Midwest Wholesale, Inc., a products wholesaler, since 1997
and a director of that company since 1970.

     Lee Liu has served as a director of our company since April 1998. He was
elected a director and Chairman of the Board of Alliant Energy Corporation in
April 1998. Prior to that time, Mr. Liu was Chairman of the Board and Chief
Executive Officer of IES Industries Inc. and IES Utilities Inc.

     Katherine C. Lyall has served as a director since 1994. Ms. Lyall has
served as President of the University of Wisconsin System since April 1992.

                                       18
<PAGE>   20

     Arnold M. Nemirow has served as a director since 1991. Mr. Nemirow is
Chairman, President and Chief Executive Officer of Bowater Incorporated, a pulp
and paper manufacturer. Mr. Nemirow served as President, Chief Executive Officer
and director of Wausau Paper Mills Company, a pulp and paper manufacturer, from
1990 until joining Bowater Incorporated in September 1994.

     Milton E. Neshek has served as a director since 1988.  Mr. Neshek serves as
General Counsel and as a director of Kikkoman Foods, Inc., a food products
manufacturer.

     Jack R. Newman has served as a director since April 1998. Mr. Newman is a
partner of Morgan, Lewis & Bockius, an international law firm based in
Washington, D.C. Prior to January 1994, he was a partner in the law firms of
Newman & Holtzinger and Newman, Bouknight and Edgar.

     Judith D. Pyle has served as a director since 1992.  Ms. Pyle is Vice Chair
of the Pyle Group, a financial services company. Prior to assuming her current
position, Ms. Pyle served as Vice Chair and Senior Vice President of Corporate
Marketing of Rayovac Corporation, a battery and lighting products manufacturer.

     Robert D. Ray has served as a director since April 1998. Mr. Ray has served
as President of Drake University since 1998. He served as President and Chief
Executive Officer of Life Investors Insurance Co. (AEGON USA) from 1983 to 1989
and President of Blue Cross/Blue Shield (Wellmark) from 1989 until his
retirement in 1996. Prior to that time, Mr. Ray served as Governor of the State
of Iowa for fourteen years.

     Robert W. Schlutz has served as a director since April 1998. Mr. Schlutz is
President of Schlutz Enterprises, a diversified farming and retailing business.

     Wayne H. Stoppelmoor has served as a director since April 1998. Mr.
Stoppelmoor has also served as Vice Chairman of the Board of Alliant Energy
Corporation since April 1998. Prior to that time, Mr. Stoppelmoor served as
Chairman, President and Chief Executive Officer of Interstate Power Company. He
retired as President of Interstate Power Company in 1996 and as Chief Executive
Officer in 1997.

     Anthony R. Weiler has served as a director since April 1998. Mr. Weiler has
been Senior Vice President of Heilig-Meyers Company, a national furniture
retailer, since 1995. He was previously Chairman and Chief Executive Officer of
Chittenden & Eastman Company, a national manufacturer of mattresses.

     All of our directors also serve as directors of Alliant Energy Corporation,
IES Utilities Inc., Interstate Power Company and Wisconsin Power and Light
Company. Messrs. Liu and Davis have employment agreements and Mr. Stoppelmoor
has a consulting agreement with Alliant Energy Corporation pursuant to which
their terms of office are established. All of our other executive officers have
no definite terms of office and serve at the pleasure of our Board of Directors.
None of our executive officers or directors are related to any other executive
officers or directors.

                                       19
<PAGE>   21

                    DESCRIPTION OF OUTSTANDING INDEBTEDNESS

     The following is information concerning our indebtedness other than the
existing senior notes.

     We are a party to a 3-Year Credit Agreement with various banking
institutions. This agreement extends through October 2000, with one-year
extensions available upon agreement by the parties. We also use unused borrowing
availability under this agreement to support our commercial paper program. A
combined maximum of $450 million of borrowings under this agreement and the
commercial paper program may be outstanding at any time. Interest rates and
maturities are set at the time of borrowing. The rates are based upon quoted
market prices and the maturities are less than one year. At September 30, 1999,
we had no direct borrowings and $329.5 million of commercial paper outstanding
and backed by this facility, with interest rates ranging from 5.42% to 5.70% and
maturities ranging from 7 to 52 days. We intend to continue issuing commercial
paper backed by this facility. No conditions existed at September 30, 1999 that
would prevent the issuance of commercial paper or direct borrowings on our bank
lines.

     We are also a party to a 364-Day Credit Agreement with various banking
institutions. This agreement extends through October 16, 2000, with 364-day
extensions available upon agreement by the parties. We also use the unborrowed
portion of this agreement to support our commercial paper program. A combined
maximum of $150 million of borrowings under this agreement and commercial paper
backed by this facility may be outstanding at any one time. Interest rates and
maturities are set at the time of borrowing. The rates are based upon quoted
market prices and the maturities are less than one year. There were no
borrowings under this facility and no commercial paper backed by this facility
outstanding at September 30, 1999.

     At September 30, 1999, we had two interest rate swap agreements
outstanding, each with a notional amount of $100 million. These agreements
expire in April 2000, with the bank having a one-year renewal option under one
of the agreements. We entered into these agreements to reduce the impact of
changes in variable interest rates by converting variable rate borrowings into
fixed rate borrowings. Accordingly, these agreements require us to pay a fixed
rate and receive a variable rate. If we terminated the agreements at September
30, 1999, we would have had to make payments of approximately $228,125.

                                       20
<PAGE>   22

                               THE EXCHANGE OFFER

PURPOSE AND EFFECT; REGISTRATION RIGHTS

     We sold the existing senior notes on November 9, 1999 in transactions
exempt from the registration requirements of the Securities Act. Therefore, the
existing senior notes are subject to significant restrictions on resale. In
connection with the issuance of the existing senior notes, we entered into a
registration rights agreement, which required that we and Alliant Energy
Corporation:

     -  file with the SEC a registration statement under the Securities Act
        relating to the exchange offer and the issuance and delivery of new
        senior notes in exchange for the existing senior notes;

     -  use our reasonable best efforts to cause the SEC to declare the exchange
        offer registration statement effective under the Securities Act; and

     -  use our reasonable best efforts to consummate the exchange offer not
        later than 45 days following the effective date of the exchange offer
        registration statement.

     If you participate in the exchange offer, you will, with limited
exceptions, receive new senior notes that are freely tradeable and not subject
to restrictions on transfer. You should read this prospectus under the heading
"-- Resales of New Senior Notes" for more information relating to your ability
to transfer new senior notes.

     If you are eligible to participate in the exchange offer and do not tender
your existing senior notes, you will continue to hold the untendered existing
senior notes, which will continue to be subject to restrictions on transfer
under the Securities Act.

     The exchange offer is intended to satisfy our exchange offer obligations
under the registration rights agreement. The above summary of the registration
rights agreement is not complete and is subject to, and qualified by reference
to, all the provisions of the registration rights agreement. A copy of the
registration rights agreement has been filed as an exhibit to the registration
statement that includes this prospectus.

TERMS OF THE EXCHANGE OFFER

     We are offering to exchange $250,000,000 in aggregate principal amount of
our 7 3/8% Senior Notes due 2009 that have been registered under the Securities
Act for a like principal amount of our outstanding unregistered 7 3/8% Senior
Notes due 2009.

     Upon the terms and subject to the conditions set forth in this prospectus
and in the accompanying letter of transmittal, we will accept all existing
senior notes validly tendered and not withdrawn before 5:00 p.m., New York City
time, on the expiration date of the exchange offer. We will issue $1,000
principal amount of new senior notes in exchange for each $1,000 principal
amount of outstanding existing senior notes we accept in the exchange offer. You
may tender some or all of your existing senior notes under the exchange offer.
However, the existing senior notes are issuable in authorized denominations of
$1,000 and integral multiples thereof. Accordingly, existing senior notes may be
tendered only in denominations of $1,000 and integral multiples thereof. The
exchange offer is not conditioned upon any minimum amount of original notes
being tendered.

     The form and terms of the new senior notes will be the same as the form and
terms of the existing senior notes, except that:

     - the new senior notes will be registered with the SEC and thus will not be
       subject to the restrictions on transfer or bear legends restricting their
       transfer;

     - all of the new senior notes will be represented by global notes in
       book-entry form unless exchanged for notes in definitive certificated
       form under the limited circumstances described under "Description of the
       New Senior Notes -- Book-Entry Procedures and Form;" and

     - the new senior notes will not provide for the payment of additional
       interest under circumstances relating to the timing of the exchange
       offer.
                                       21
<PAGE>   23

     The new senior notes will evidence the same debt as the existing senior
notes and will be issued under, and be entitled to the benefits of, the
indenture, as supplemented, governing the existing senior notes.

     The new senior notes will accrue interest from the most recent date to
which interest has been paid on the existing senior notes or, if no interest has
been paid, from the date of issuance of the existing senior notes. Accordingly,
registered holders of new senior notes on the record date for the first interest
payment date following the completion of the exchange offer will receive
interest accrued from the most recent date to which interest has been paid on
the existing senior notes or, if no interest has been paid, from the date of
issuance of the existing senior notes. However, if that record date occurs prior
to completion of the exchange offer, then the interest payable on the first
interest payment date following the completion of the exchange offer will be
paid to the registered holders of the existing senior notes on that record date.

     In connection with the exchange offer, you do not have any appraisal or
dissenters' rights under the Wisconsin Business Corporation Law or the
indenture, as supplemented. We intend to conduct the exchange offer in
accordance with the registration rights agreement and the applicable
requirements of the Securities Exchange Act of 1934 and the rules and
regulations of the SEC.

     We will be deemed to have accepted validly tendered existing senior notes
when, as and if we have given oral or written notice of our acceptance to the
exchange agent. The exchange agent will act as agent for the tendering holders
for the purpose of receiving the new senior notes from us.

     If we do not accept any tendered existing senior notes because of an
invalid tender or for any other reason, we will return certificates for any
unaccepted existing senior notes without expense to the tendering holder as
promptly as practicable after the expiration date.

EXPIRATION DATE; AMENDMENTS

     The exchange offer will expire at 5:00 p.m., New York City time, on
          , 2000, unless we, in our sole discretion, extend the exchange offer.

     If we determine to extend the exchange offer, we will notify the exchange
agent of any extension by oral or written notice and give each registered holder
notice of the extension by means of a press release or other public announcement
before 9:00 a.m., New York City time, on the next business day after the
previously scheduled expiration date.

     We reserve the right, in our sole discretion, to delay accepting any
existing senior notes, to extend the exchange offer or to amend or terminate the
exchange offer if any of the conditions described below under "-- Conditions"
have not been satisfied or waived by giving oral or written notice to the
exchange agent of the delay, extension, amendment or termination. Further, we
reserve the right, in our sole discretion, to amend the terms of the exchange
offer in any manner. We will notify you as promptly as practicable of any
extension, amendment or termination.

PROCEDURES FOR TENDERING EXISTING SENIOR NOTES

     Any tender of existing senior notes that is not withdrawn prior to the
expiration date will constitute a binding agreement between the tendering holder
and us upon the terms and subject to the conditions set forth in this prospectus
and in the accompanying letter of transmittal. A holder who wishes to tender
existing senior notes in the exchange offer must do either of the following:

     -  properly complete, sign and date the letter of transmittal, including
        all other documents required by the letter of transmittal; have the
        signature on the letter of transmittal guaranteed if the letter of
        transmittal so requires; and deliver that letter of transmittal and
        other required documents to the exchange agent at the address listed
        below under "-- Exchange Agent" on or before the expiration date; or

     -  if the existing senior notes are tendered under the book-entry transfer
        procedures described below, transmit to the exchange agent on or before
        the expiration date an agent's message.



                                       22
<PAGE>   24

     In addition, one of the following must occur:

     -  the exchange agent must receive certificates representing your existing
        senior notes, along with the letter of transmittal, on or before the
        expiration date; or

     -  the exchange agent must receive a timely confirmation of book-entry
        transfer of the existing senior notes into the exchange agent's account
        at DTC under the procedure for book-entry transfers described below,
        along with the letter of transmittal or a properly transmitted agent's
        message, on or before the expiration date; or

     -  the holder must comply with the guaranteed delivery procedures described
        below.

     The term "agent's message" means a message, transmitted by a book-entry
transfer facility to and received by the exchange agent and forming a part of
the book-entry confirmation, which states that the book-entry transfer facility
has received an express acknowledgement from the tendering participant stating
that the participant has received and agrees to be bound by the letter of
transmittal and that we may enforce the letter of transmittal against the
participant.

     The method of delivery of existing senior notes, the letter of transmittal
and all other required documents to the exchange agent is at your election and
risk. Rather than mail these items, we recommend that you use an overnight or
hand delivery service. In all cases, you should allow sufficient time to assure
timely delivery to the exchange agent before the expiration date. Do not send
letters of transmittal or existing senior notes to us.

     Generally, an eligible institution must guarantee signatures on a letter of
transmittal or a notice of withdrawal unless the existing senior notes are
tendered:

     -  by a registered holder of the existing senior notes who has not
        completed the box entitled "Special Issuance Instructions" or "Special
        Delivery Instructions" on the letter of transmittal; or

     -  for the account of an eligible institution.

     If signatures on a letter of transmittal or a notice of withdrawal are
required to be guaranteed, the guarantee must be by a firm which is:

     -  a member of a registered national securities exchange;

     -  a member of the National Association of Securities Dealers, Inc.;

     -  a commercial bank or trust company having an office or correspondent in
        the United States; or

     -  another "eligible institution" within the meaning of Rule 17Ad-15 under
        the Securities Exchange Act.

     If the letter of transmittal is signed by a person other than the
registered holder of any outstanding existing senior notes, the original notes
must be endorsed or accompanied by appropriate powers of attorney. The power of
attorney must be signed by the registered holder exactly as the registered
holder(s) name(s) appear(s) on the existing senior notes and an eligible
institution must guarantee the signature on the power of attorney.

     If the letter of transmittal, or any existing senior notes or powers of
attorney are signed by trustees, executors, administrators, guardians,
attorneys-in-fact, officers of corporations or others acting in a fiduciary or
representative capacity, these persons should so indicate when signing. Unless
waived by us, they should also submit evidence satisfactory to us of their
authority to so act.

     If you wish to tender existing senior notes that are registered in the name
of a broker, dealer, commercial bank, trust company or other nominee, you should
promptly instruct the registered holder to tender on your behalf. If you wish to
tender on your behalf, you must, before completing the procedures for tendering
existing senior notes, either register ownership of the existing senior notes in
your name or obtain a properly completed bond power from the registered holder.
The transfer of registered ownership may take considerable time.


                                       23
<PAGE>   25

     We will determine in our sole discretion all questions as to the validity,
form, eligibility, including time of receipt, and acceptance of existing senior
notes tendered for exchange. Our determination will be final and binding on all
parties. We reserve the absolute right to reject any and all tenders of existing
senior notes not properly tendered or existing senior notes our acceptance of
which might, in the judgment of our counsel, be unlawful. We also reserve the
absolute right to waive any defects, irregularities or conditions of tender as
to any particular existing senior notes. Our interpretation of the terms and
conditions of the exchange offer, including the instructions in the letter of
transmittal, will be final and binding on all parties. Unless waived, any
defects or irregularities in connection with tenders of existing senior notes
must be cured within the time period we determine. Neither we, the exchange
agent nor any other person will incur any liability for failure to give you
notification of defects or irregularities with respect to tenders of your
existing senior notes.

     By tendering, you will represent to us that, among other things:

     -  the new senior notes acquired in the exchange offer are being acquired
        in the ordinary course of business of the person receiving the new
        senior notes;

     -  neither you nor any other person receiving your new senior notes has any
        arrangement or understanding with any person to participate in the
        distribution of the new senior notes; and

     -  neither you nor any other person receiving your new senior notes is our
        "affiliate," as defined under Rule 405 of the Securities Act.

     If you or the person receiving your new senior notes is our "affiliate," as
defined under Rule 405 of the Securities Act, or is participating in the
exchange offer for the purpose of distributing the new senior notes, you or that
other person cannot rely on the applicable interpretations of the staff of the
SEC, cannot tender your existing senior notes in the exchange offer and must
comply with the registration and prospectus delivery requirements of the
Securities Act in any resale transaction.

     If you are a broker-dealer and you will receive new senior notes for your
own account in exchange for the existing senior notes, where such existing
senior notes were acquired as a result of market-making activities or other
trading activities, you must acknowledge that you will deliver a prospectus in
connection with any resale of the new senior notes.

ACCEPTANCE OF EXISTING SENIOR NOTES FOR EXCHANGE; DELIVERY OF NEW SENIOR NOTES

     Upon satisfaction of all conditions to the exchange offer, we will accept,
promptly after the expiration date, all existing senior notes properly tendered
and will issue the new senior notes promptly after acceptance of the existing
senior notes.

     For purposes of the exchange offer, we will be deemed to have accepted
properly tendered existing senior notes for exchange when, as and if we have
given oral or written notice of that acceptance to the exchange agent. For each
existing senior note accepted for exchange, you will receive a new senior note
having a principal amount equal to that of the surrendered existing senior note.

     In all cases, we will issue new senior notes for existing senior notes that
we have accepted for exchange under the exchange offer only after the exchange
agent timely receives:

     - certificates for your existing senior notes or a timely confirmation of
       book-entry transfer of your existing senior notes into the exchange
       agent's account at DTC; and

     - a properly completed and duly executed letter of transmittal and all
       other required documents or a properly transmitted agent's message.

     If we do not accept any tendered existing senior notes for any reason set
forth in the terms of the exchange offer or if you submit existing senior notes
for a greater principal amount than you desire to exchange, we will return the
unaccepted or non-exchanged existing senior notes without expense to you. In the
case of existing senior notes tendered by book-entry transfer into the exchange
agent's account at DTC

                                       24
<PAGE>   26

under the book-entry procedures described below, we will credit the
non-exchanged existing senior notes to your account maintained with DTC.

BOOK-ENTRY TRANSFER

     We understand that the exchange agent will make a request within two
business days after the date of this prospectus to establish accounts for the
existing senior notes at DTC for the purpose of facilitating the exchange offer,
and any financial institution that is a participant in DTC's system may make
book-entry delivery of existing senior notes by causing DTC to transfer the
existing senior notes into the exchange agent's account at DTC in accordance
with DTC's procedures for transfer. Although delivery of existing senior notes
may be effected through book-entry transfer at DTC, the exchange agent must
receive a properly completed and duly executed letter of transmittal with any
required signature guarantees, or an agent's message instead of a letter of
transmittal, and all other required documents at its address listed below under
"-- Exchange Agent" on or before the expiration date, or if you comply with the
guaranteed delivery procedures described below, within the time period provided
under those procedures.

GUARANTEED DELIVERY PROCEDURES

     If you wish to tender your existing senior notes and your existing senior
notes are not immediately available, or you cannot deliver your existing senior
notes, the letter of transmittal or any other required documents or comply with
DTC's procedures for transfer before the expiration date, then you may
participate in the exchange offer if:

     -  the tender is made through an eligible institution;

     -  before the expiration date, the exchange agent receives from the
        eligible institution a properly completed and duly executed notice of
        guaranteed delivery, substantially in the form provided by us, by
        facsimile transmission, mail or hand delivery, containing (a) the name
        and address of the holder and the principal amount of existing senior
        notes tendered, (b) a statement that the tender is being made thereby,
        and (c) a guarantee that within three New York Stock Exchange trading
        days after the expiration date, the certificates representing the
        existing senior notes in proper form for transfer or a book-entry
        confirmation and any other documents required by the letter of
        transmittal will be deposited by the eligible institution with the
        exchange agent; and

     -  the exchange agent receives the properly completed and executed letter
        of transmittal as well as certificates representing all tendered
        existing senior notes in proper form for transfer, or a book-entry
        confirmation, and all other documents required by the letter of
        transmittal within three New York Stock Exchange trading days after the
        expiration date.

WITHDRAWAL RIGHTS

     You may withdraw your tender of existing senior notes at any time before
the exchange offer expires.

     For a withdrawal to be effective, the exchange agent must receive a written
notice of withdrawal at its address listed below under "-- Exchange Agent." The
notice of withdrawal must:

     -  specify the name of the person who tendered the existing senior notes to
        be withdrawn;

     -  identify the existing senior notes to be withdrawn, including the
        principal amount, or, in the case of existing senior notes tendered by
        book-entry transfer, the name and number of the DTC account to be
        credited, and otherwise comply with the procedures of DTC; and

     -  if certificates for existing senior notes have been transmitted, specify
        the name in which those existing senior notes are registered if
        different from that of the withdrawing holder.

     If you have delivered or otherwise identified to the exchange agent the
certificates for existing senior notes, then, before the release of such
certificates, you must also submit the serial numbers of the

                                       25
<PAGE>   27

particular certificates to be withdrawn and a signed notice of withdrawal with
the signatures guaranteed by an eligible institution, unless the holder is an
eligible institution.

     We will determine in our sole discretion all questions as to the validity,
form and eligibility, including time of receipt, of notices of withdrawal. Our
determination will be final and binding on all parties. Any existing senior
notes so withdrawn will be deemed not to have been validly tendered for purposes
of the exchange offer. We will return any existing senior notes that have been
tendered but that are not exchanged for any reason to the holder, without cost,
as soon as practicable after withdrawal, rejection of tender or termination of
the exchange offer. In the case of existing senior notes tendered by book-entry
transfer into the exchange agent's account at DTC, the existing senior notes
will be credited to an account maintained with DTC for the existing senior
notes. You may retender properly withdrawn existing senior notes by following
one of the procedures described under "-- Procedures for Tendering Existing
Senior Notes" at any time on or before the expiration date.

CONDITIONS

     Notwithstanding any other term of the exchange offer, we will not be
required to accept for exchange, or to exchange new senior notes for, any
existing senior notes if:

     -  the exchange offer, or the making of any exchange by a holder of
        existing senior notes, would violate any applicable law or applicable
        interpretation by the staff of the SEC;

     -  any action or proceeding is instituted or threatened in any court or by
        or before any governmental agency with respect to the exchange offer
        which, in our judgment, would reasonably be expected to impair our
        ability to proceed with the exchange offer; or

     -  at the time of the consummation of the exchange offer, the interest rate
        payable on the new senior notes would be greater than 300 basis points
        over the yield to maturity of a United States Treasury obligation with
        the same term as the new senior notes.

     The conditions listed above are for our sole benefit and we may assert them
regardless of the circumstances giving rise to any condition. Subject to
applicable law, we may waive these conditions in our discretion in whole or in
part at any time and from time to time. If we fail at any time to exercise any
of the above rights, the failure will not be deemed a waiver of those rights,
and those rights will be deemed ongoing rights which may be asserted at any time
and from time to time.

EXCHANGE AGENT

     Firstar Bank, N.A. is the exchange agent for the exchange offer. You should
direct any questions and requests for assistance and requests for additional
copies of this prospectus, the letter of transmittal or the notice of guaranteed
delivery to the exchange agent addressed as follows:

     By Hand, Overnight Mail, Courier, or Registered or Certified Mail:

        Firstar Bank, N.A.
        1555 North RiverCenter Drive
        Suite 301
        Milwaukee, Wisconsin 53212
        Attention: Ms. Pamela Warner

     By Facsimile:

        (414) 276-4226
        Attention: Ms. Pamela Warner

     Delivery of the letter of transmittal to an address other than as listed
above or transmission via facsimile other than as listed above will not
constitute a valid delivery of the letter of transmittal.

                                       26
<PAGE>   28

FEES AND EXPENSES

     We will pay the expenses of the exchange offer. We will not make any
payments to brokers, dealers or others soliciting acceptances of the exchange
offer. We are making the principal solicitation by mail; however, our officers
and employees may make additional solicitations by facsimile transmission,
e-mail, telephone or in person. You will not be charged a service fee for the
exchange of your senior notes, but we may require you to pay any transfer or
similar government taxes in certain circumstances.

TRANSFER TAXES

     You will not be obligated to pay any transfer taxes, unless you instruct us
to register new senior notes in the name of, or request that existing senior
notes not tendered or not accepted in the exchange offer be returned to, a
person other than the registered tendering holder.

ACCOUNTING TREATMENT

     We will record the new senior notes at the same carrying values as the
existing senior notes, which is the aggregate principal amount of the existing
senior notes, as reflected in our accounting records on the date of exchange.
Accordingly, we will not recognize any gain or loss on the exchange of senior
notes. We will amortize the expenses of the offer over the term of the new
senior notes.

CONSEQUENCES OF FAILURE TO EXCHANGE EXISTING SENIOR NOTES

     If you are eligible to participate in the exchange offer but do not tender
your existing senior notes, you will not have any further registration rights.
Your existing senior notes will continue to be subject to restrictions on
transfer. Accordingly, you may resell the existing senior notes that are not
exchanged only:

     - to us;

     - so long as the existing senior notes are eligible for resale under Rule
       144A under the Securities Act, to a person whom you reasonably believe is
       a "qualified institutional buyer" within the meaning of Rule 144A
       purchasing for its own account or for the account of a qualified
       institutional buyer in a transaction meeting the requirements of Rule
       144A;

     - in accordance with Rule 144 under the Securities Act or another exemption
       from the registration requirements of the Securities Act;

     - to an institutional accredited investor (as defined in Rule 501(a)(1),
       (2), (3) or (7) under the Securities Act) that is acquiring the existing
       senior notes for its own account or for the account of an institutional
       accredited investor for investment purposes and not with a view to, or
       for offer or sale in connection with, any distribution in violation of
       the Securities Act; or

     - under any effective registration statement under the Securities Act;

in each case in accordance with all other applicable securities laws. We do not
intend to register the existing senior notes under the Securities Act.

RESALES OF NEW SENIOR NOTES

     We are making the exchange offer in reliance on the position of the staff
of the SEC as set forth in interpretive letters addressed to third parties in
other transactions. However, we have not sought our own interpretive letter, and
there can be no assurance that the staff of the SEC would make a similar
determination with respect to the exchange offer as it has in the interpretive
letters addressed to third parties. Based on these interpretations by the staff
of the SEC, and except as provided below, we believe that new senior notes may
be offered for resale, resold and otherwise transferred by a holder that
participates in the exchange offer and is not a broker-dealer without further
compliance with the registration and prospectus delivery provisions of the
Securities Act. To receive new senior notes that are freely tradeable, a holder
must acquire the new senior notes in the ordinary course of its business and may

                                       27
<PAGE>   29

not participate, or have any arrangement or understanding with any person to
participate, in the distribution (within the meaning of the Securities Act) of
the existing senior notes or the new senior notes. Holders wishing to
participate in the exchange offer must make the representations described in
" -- Procedures for Tendering Existing Senior Notes" above.

     Any holder of existing senior notes:

     - who is our "affiliate," as defined in Rule 405 under the Securities Act;

     - who did not acquire the new senior notes in the ordinary course of its
       business; or

     - who intends to participate, or has an arrangement or understanding with
       any person to participate, in a distribution (within the meaning of the
       Securities Act) of the existing senior notes or the new senior notes,

will be subject to separate restrictions. Each holder in any of the above
categories:

     - will not be ably to rely on the interpretations of the staff of the SEC
       in the above-mentioned interpretative letters;

     - will not be permitted or entitled to tender existing senior notes in the
       exchange offer; and

     - must comply with the registration and prospectus delivery requirements of
       the Securities Act in connection with any sale or other transfer of
       existing senior notes unless such sale is made pursuant to an exemption
       from such requirements.

     In addition, if you are a broker-dealer holding existing senior notes
acquired for your own account, then you may be deemed a statutory "underwriter"
within the meaning of the Securities Act in connection with any resales of your
new senior notes. Each broker-dealer that receives new senior notes for its own
account pursuant to the exchange offer must acknowledge that it acquired the
existing senior notes for its own account as a result of market-making
activities or other trading activities and must agree that it will deliver a
prospectus meeting the requirements of the Securities Act in connection with any
resale of those new senior notes. The letter of transmittal states that by
making the above acknowledgement and by delivering a prospectus, a broker-dealer
will not be deemed to admit that it is an "underwriter" within the meaning of
the Securities Act.

     Based on the position taken by the staff of the SEC in the interpretative
letters referred to above, we believe that broker-dealers who acquired existing
senior notes for their own accounts, as a result of market-making or other
trading activities ("participating broker-dealers") may fulfill their prospectus
delivery requirements with respect to the new senior notes received upon the
exchange of existing senior notes (other than existing senior notes that
represent an unsold allotment from the original sale of the existing senior
notes) with a prospectus meeting the requirements of the Securities Act, which
may be the prospectus prepared for an exchange offer so long as it contains a
description of the plan of distribution with respect to the sale of such new
senior notes. Accordingly, this prospectus, as it may be amended or
supplemented, may be used by a participating broker-dealer in connection with
resales of new senior notes received in exchange for existing senior notes where
such existing senior notes were acquired by such participating broker-dealer for
its own account as a result of market-making or other trading activities. See
"Plan of Distribution." However, a participating broker-dealer who intends to
use this prospectus in connection with the resale of new senior notes received
in exchange for existing senior notes pursuant to the exchange offer must notify
us, or cause us to be notified, on or before the expiration date of the exchange
offer, that it is a participating broker-dealer. Such notice may be given in the
space provided for that purpose in the letter of transmittal or may be delivered
to the exchange agent at the address set forth above under " --  Exchange
Agent." Any participating broker-dealer who is an "affiliate" of ours may not
rely on such interpretive letters and must comply with the registration and
prospectus delivery requirements of the Securities Act in connection with any
resale transaction.

                                       28
<PAGE>   30

                      DESCRIPTION OF THE NEW SENIOR NOTES

     The existing senior notes were, and the new senior notes will be, issued
under and governed by an Indenture, as supplemented and amended by the First
Supplemental Indenture dated as of November 4, 1999 (the "Supplemental
Indenture," and collectively, the "Indenture"), between us and Firstar Bank,
N.A., as trustee and paying agent (the "Trustee"). The following summary of
certain provisions of the Indenture, the new senior notes and the guarantees is
not complete, and is qualified in its entirety by reference to the provisions of
the Indenture. A copy of the Indenture and the Supplemental Indenture have been
filed as exhibits to the registration statement that includes this prospectus.
The holders of new senior notes are entitled to the benefits of, are bound by,
and are deemed to have notice of, all the provisions of the Indenture. Wherever
defined terms of the Indenture are referred to, such defined terms are
incorporated herein by reference.

GENERAL

     The Indenture does not limit the aggregate principal amount of debt
securities that may be issued thereunder and provides that debt securities may
be issued from time to time in one or more series as provided in a supplemental
indenture or Board Resolution. The new senior notes will be unconditionally
guaranteed by Alliant Energy Corporation, will be issued in the aggregate
principal amount of $250,000,000 and will mature on November 9, 2009, at their
principal amount (unless previously redeemed).

     We will pay interest on the new senior notes at a rate of 7 3/8% per annum
from the most recent date to which interest has been paid on the existing senior
notes or, if no interest has been paid, from the date of issuance of the
existing senior notes. We will pay interest on the new senior notes semiannually
in arrears on May 9 and November 9 of each year, commencing on May 9, 2000,
until the principal amount has been paid or made available for payment, to the
persons in whose names the new senior notes are registered at the close of
business on May 1 or November 1, as the case may be, before each interest
payment date. Interest on the new senior notes will be computed on the basis of
a 360-day year of twelve 30-day months. The principal of and interest on the new
senior notes will be payable in U.S. dollars or in such other coin or currency
of the United States that at the time of payment is legal tender for the payment
of public and private debts.

RANKING

     The new senior notes will be senior, unsecured and unsubordinated
obligations of ours ranking equally and ratably with all our other senior,
unsecured and unsubordinated obligations. The new senior notes will be
unconditionally guaranteed by Alliant Energy Corporation. The guarantees will be
unsecured obligations of Alliant Energy Corporation and will rank equally with
all other unsecured and unsubordinated indebtedness of Alliant Energy
Corporation. Because we are a holding company and conduct substantially all of
our operations through our subsidiaries, the rights of our creditors, including
those under the new senior notes, to participate in any distributions of the
assets of any of our subsidiaries or joint ventures, upon liquidation or
reorganization or otherwise, are necessarily subject, and therefore will be
effectively subordinated, to the prior claims of creditors of any of our
subsidiaries or joint ventures (including trade creditors and holders of
indebtedness issued by such subsidiary or joint venture), except to the extent
our claims as a creditor may be recognized.

     In addition, because Alliant Energy Corporation is a holding company which
conducts substantially all of its operations through subsidiaries, including us,
the right of Alliant Energy Corporation, and hence the right of creditors of
Alliant Energy Corporation (including holders of the new senior notes through
the guarantees), to participate in any distribution of assets of any subsidiary
upon its liquidation or reorganization or otherwise is necessarily subject to
the prior claims of creditors of such subsidiaries, except to the extent that
claims of Alliant Energy Corporation itself as a creditor of the subsidiary may
be recognized.

                                       29
<PAGE>   31

     The new senior notes will also be effectively subordinated to all of our
future secured indebtedness and the related guarantees will be effectively
subordinated to all future secured indebtedness of Alliant Energy Corporation.

BOOK-ENTRY PROCEDURES AND FORM

  Global Notes: Book-Entry Form

     Except as provided below, the new senior notes will be issued in fully
registered book-entry form and will be represented by one or more global notes.
The global notes will be deposited with, or on behalf of, The Depositary Trust
Company of New York City ("DTC") and registered in the name of a nominee of DTC.

     We expect that pursuant to procedures established by DTC (a) upon the
issuance of the new senior notes in the form of one or more global notes, DTC or
its custodian will credit, on its internal system, the principal amount of new
senior notes of the individual beneficial interests represented by these global
notes to the respective accounts of persons who have accounts with DTC
("participants") and (b) ownership of beneficial interests in the global notes
will be shown on, and the transfer of this ownership will be effected only
through, records maintained by DTC or its nominee (with respect to interests of
participants) and the records of participants (with respect to interests of
persons other than participants). Holders of senior notes may hold their
interests in the global notes directly through DTC if they are participants in
this system, or indirectly through organizations which are participants in this
system. The laws of some states of the United States may require that certain
purchasers of securities take physical delivery of the new senior notes in
definitive certificated form. Such limits and such laws may impair the ability
of such purchasers to own, transfer or pledge interests in the global notes.

     So long as DTC, or its nominee, is the registered owner or holder of new
senior notes, DTC or its nominee, as the case may be, will be considered the
sole owner or holder of new senior notes represented by the global notes for all
purposes under the Indenture. No beneficial owner of an interest in the global
notes will be able to transfer that interest except in accordance with DTC's
procedures, in addition to those provided for under the Indenture with respect
to the new senior notes.

     Payments of the principal of and premium, if any, and interest on the
global notes will be made to DTC or its nominee, as the case may be, as the
registered owner thereof. None of us, the Trustee or any paying agent will have
any responsibility or liability for any aspect of the records relating to or
payments made on account of beneficial ownership interests in the global notes
or for maintaining, supervising or reviewing any records relating to such
beneficial ownership interest.

     We expect that DTC or its nominee, upon receipt of any payment of principal
of and premium, if any, and interest on the global notes, will credit
participants' accounts with payments in amounts proportionate to their
respective beneficial interests in the principal amount of the global notes as
shown on the records of DTC or its nominee. We also expect that payments by
participants to owners of beneficial interests in the global notes held through
such participants will be governed by standing instructions and customary
practice, as is now the case with securities held for the accounts of customers
registered in the names of nominees for such customers. These payments will be
the responsibility of such participants. Transfers between participants in DTC
will be effected in the ordinary way through DTC's settlement system in
accordance with DTC rules and will be settled in same day funds.

     DTC has advised us that it will take any action permitted to be taken by a
holder of new senior notes only at the direction of one or more participants to
whose account the DTC interests in the global notes are credited and only in
respect of such portion of the aggregate principal amount of new senior notes as
to which such participant or participants has or have given such direction.

     DTC has advised us as follows: DTC is a limited purpose trust company
organized under the laws of the State of New York, a member of the Federal
Reserve System, a "clearing corporation" within the meaning of the Uniform
Commercial Code and a "clearing agency" registered pursuant to the provisions of
Section 17A of the Securities Exchange Act of 1934. DTC was created to hold
securities for its
                                       30
<PAGE>   32

participants and facilitate the clearance and settlement of securities
transactions between participants through electronic book-entry changes in
accounts of its participants, thereby eliminating the need for physical movement
of certificates. Participants include securities brokers and dealers, banks,
trust companies and clearing corporations and certain other organizations.
Indirect access to the DTC system is available to others such as banks, brokers,
dealers and trust companies that clear through or maintain a custodial
relationship with a participant, either directly or indirectly ("indirect
participants").

     Although DTC has agreed to the foregoing procedures in order to facilitate
transfers of interests in the global notes among participants of DTC, it is
under no obligation to perform such procedures, and such procedures may be
discontinued at any time. None of us, the Trustee or any of our respective
agents will have any responsibility for the performance by DTC or its
participants or indirect participants of their respective obligations under the
rules and procedures governing their operations, including maintaining,
supervising or reviewing the records relating to, payments made on account of,
beneficial ownership interests in global notes.

     We have been informed by DTC that its management is aware that some
computer applications, systems and the like for processing data that are
dependent upon calendar dates, including dates before, on and after January 1,
2000, may encounter "Year 2000 problems." We have also been informed by DTC that
it has informed its participants and other members of the financial community
that it has developed and is implementing a program so that its systems, as the
same relates to the timely payment of distributions (including principal and
interest payments) to securityholders, book-entry deliveries and settlement of
trades within DTC, continue to function appropriately. According to DTC, this
program includes a technical assessment and a remediation plan, each of which is
complete. Additionally, DTC has informed us that its plan includes a testing
phase, which is expected to be completed within appropriate time frames.

     However, we have been informed by DTC that its ability to perform properly
its services is also dependent upon other parties, including but not limited to
issuers and their agents, as well as third-party vendors from whom DTC licenses
software and hardware, and third-party vendors on whom DTC relies for
information or the provision of services, including telecommunication and
electrical utility service providers, among others. DTC has informed us that it
has informed its participants and other members of the financial community that
it is contacting (and will continue to contact) third-party vendors from whom
DTC acquires services to impress upon them the importance of such services being
Year 2000 compliant and determine the extent of their efforts for Year 2000
remediation (and, as appropriate, testing) of their services. In addition, DTC
has informed us that it is in the process of developing such contingency plans
as it deems appropriate.

     According to DTC, the foregoing information with respect to DTC has been
provided to its participants and other members of the financial community for
informational purposes only and is not intended to serve as a representation,
warranty or contract modification of any kind.

  Certificated Debentures

     We will issue new senior notes in certificated form in exchange for global
notes if:

     -  DTC or any successor depositary notifies us that it is unwilling or
        unable to continue as a depositary for the global notes or ceases to be
        a "clearing agency" registered under the Securities Exchange Act of 1934
        and a successor depositary is not appointed by us within 90 days of such
        notice,

     -  an Event of Default (as defined below) under the new senior notes has
        occurred and is continuing, or

     -  we determine that the new senior notes will no longer be represented by
        global notes.

     The holder of a new senior note in certificated form may transfer such note
by surrendering it at the office or agency maintained by us for such purpose in
Milwaukee, Wisconsin or New York, New York.

                                       31
<PAGE>   33

     A holder of a new senior note may request that its new senior note be
issued in certificated form and may request at any time that its interest in a
global note be exchanged for a new senior note in certificated form. New senior
notes in certificated form may also be issued in exchange for new senior notes
represented by the global notes if no successor depositary is appointed by us as
described above or in certain other circumstances set forth in the Indenture.

PURCHASE AND CANCELLATION

     We may at any time purchase new senior notes in the open market or
otherwise at any price (subject to applicable U.S. securities laws). Any
purchase by tender will be made available to all holders of new senior notes.
Any new senior notes so purchased must be promptly surrendered to the Trustee
for cancellation.

     All new senior notes that are redeemed or purchased by us will promptly be
canceled. Any new senior notes in certificated form so canceled will be
forwarded to or to the order of the Trustee and such new senior notes in
certificated form may not be reissued or resold.

COVENANTS

     Except as otherwise set forth under "-- Defeasance and Covenant Defeasance"
below, for so long as any new senior notes remain outstanding or any amount
remains unpaid on any of the new senior notes, we will comply with the terms of
the covenants set forth below.

  Payment of Principal and Interest

     We will duly and punctually pay the principal of and premium, if any, and
interest on the new senior notes in accordance with the terms of the new senior
notes and the Indenture.

  Limitation on Liens

     The Indenture provides that we will not, and we will not permit any of our
subsidiaries to issue, assume or guarantee any Debt (as defined below) if the
Debt is secured by any Lien (as defined below) upon any of our property or
assets (other than cash), without effectively securing the outstanding new
senior notes (together with any other indebtedness or obligation then existing
or thereafter created ranking equally with the new senior notes) equally and
ratably with the Debt. This limitation does not apply to:

     -  Liens in existence on the date of original issuance of the new senior
        notes;

     -  any Lien created or arising over any property or assets which we or any
        of our subsidiaries acquire, construct or create, but only if (a) the
        Lien secures only principal amounts (not exceeding the cost of the
        acquisition, construction or creation) of Debt incurred for the purposes
        of the acquisition, construction or creation of the property or assets,
        together with any costs, expenses, interest and fees incurred in
        connection with the acquisition, construction or creation of the
        property or assets or a guarantee given in connection with the
        acquisition, construction or creation of the property or assets, (b) the
        Lien is created or arises on or before 90 days after the completion of
        the acquisition, construction or creation of the property or assets and
        (c) the Lien is confined solely to the property or assets so acquired,
        constructed or created;

     -  any Lien to secure the Debt incurred by us or our subsidiaries in
        connection with a specifically identifiable project where the Lien
        relates and is confined to a property or properties (including, without
        limitation, shares or other rights of ownership in the entities which
        own such property or project) involved in such project and acquired by
        us or our subsidiaries after the date of original issuance of the senior
        notes and the recourse of the creditors in respect of the Debt is
        limited to any or all of such project and property (including as
        aforesaid);

     -  any Lien securing amounts not more than 90 days overdue or otherwise
        being contested in good faith;

                                       32
<PAGE>   34

     -  (a) rights of financial institutions to offset credit balances in
        connection with the operation of cash management programs established
        for our or any of our subsidiaries' benefit or in connection with the
        issuance of letters of credit for our or any of our subsidiaries'
        benefit; (b) any Lien securing Debt incurred by us or any of our
        subsidiaries in connection with the financing of accounts receivable;
        (c) any Lien incurred or deposits made in the ordinary course of
        business, including, but not limited to, (1) any mechanics',
        materialmen's, carriers', workmen's, vendors' or other like Liens and
        (2) any Liens securing amounts in connection with workers' compensation,
        unemployment insurance and other types of social security; (d) any Lien
        upon specific items of our or any of our subsidiaries' inventory or
        other goods and proceeds securing our or any of our subsidiaries'
        obligations in respect of bankers' acceptances issued or created to
        facilitate the purchase, shipment or storage of such inventory or other
        goods; (e) any Lien incurred or deposits made securing the performance
        of tenders, bids, leases, trade contracts (other than for borrowed
        money), statutory obligations, surety bonds, appeal bonds, government
        contracts, performance bonds, return-of-money bonds and other
        obligations of like nature incurred by us or any of our subsidiaries in
        the ordinary course of business; (f) any Lien constituted by a right of
        set off or right over a margin call account or any form of cash or cash
        collateral or any similar arrangement for obligations incurred by us or
        any of our subsidiaries in respect of the hedging or management of risks
        under transactions involving any currency or interest rate swap, cap or
        collar arrangements, forward exchange transaction, option, warrant,
        forward rate agreement, futures contract or other derivative instrument
        of any kind; (g) any Lien arising out of title retention or like
        provisions in connection with the purchase of goods and equipment by us
        or any of our subsidiaries in the ordinary course of business; and (h)
        any Lien securing reimbursement obligations under letters of credit,
        guarantees and other forms of credit enhancement given in connection
        with the purchase of goods and equipment by us or any of our
        subsidiaries in the ordinary course of business;

     -  (a) Liens on any property or assets acquired from an entity which is
        merged with or into us or any of our subsidiaries and is not created in
        anticipation of any such transaction (unless the Lien was created to
        secure or provide for the payment of any part of the purchase price of
        the entity to be acquired) and (b) any Lien on any property or assets
        existing at the time of acquisition by us or any of our subsidiaries and
        which is not created in anticipation of the acquisition (unless the Lien
        was created to secure or provide for the payment of any part of the
        purchase price of the property or assets so acquired);

     -  (a) Liens required by any contract or statute in order to permit us or
        any of our subsidiaries to perform any contract or subcontract made by
        us or any of our subsidiaries with or at the request of a governmental
        entity or any department, agency or instrumentality of a governmental
        entity, or to secure partial, progress, advance or any other payments by
        us or any of our subsidiaries to a governmental unit under the
        provisions of any contract or statute; (b) any Lien securing industrial
        revenue, development or similar bonds issued by us or any of our
        subsidiaries or for our or any of our subsidiaries' benefit, provided
        that the industrial revenue, development or similar bonds are
        nonrecourse to us or any of our subsidiaries; and (c) any Lien securing
        taxes or assessments or other applicable governmental charges or levies;

     -  (a) any Lien which arises under any order of attachment, distraint or
        similar legal process arising in connection with court proceedings and
        any Lien which secures the reimbursement obligation for any bond
        obtained in connection with an appeal taken in any court proceeding, so
        long as the execution or other enforcement of the Lien arising in
        connection with such legal process is effectively stayed and the claims
        secured by the Lien are being contested in good faith and, if
        appropriate, by appropriate legal proceedings, or any Lien in favor of a
        plaintiff or defendant in any action before a court or tribunal as
        security for costs or expenses; or (b) any Lien arising by operation of
        law or by order of a court or tribunal or any Lien arising by an
        agreement of similar effect, including, without limitation, judgment
        liens; or

     -  any extension, renewal or replacement (or successive extensions,
        renewals or replacements), as a whole or in part, of any Liens referred
        to in the clauses above, for amounts not exceeding the


                                       33

<PAGE>   35

        principal amount of the Debt secured by the Lien so extended, renewed or
        replaced, so long as the extension, renewal or replacement Lien is
        limited to all or a part of the same property or assets that were
        covered by the Lien that was extended, renewed or replaced (plus
        improvements on such property or assets).

     Although the Indenture limits our and our subsidiaries' ability to incur
Liens as set forth above, the Indenture nevertheless provides that we or our
subsidiaries may create or permit to subsist Liens over any of our and our
subsidiaries' property or assets so long as the aggregate amount of Debt secured
by all Liens that we or our subsidiaries incur (excluding the amount of Debt
secured by Liens set forth in the clauses above) does not exceed 10% of Alliant
Energy Corporation's Consolidated Net Tangible Assets.

     "Consolidated Net Tangible Assets" is defined in the Indenture as the total
of all assets (including revaluations thereof as a result of commercial
appraisals, price level restatement or otherwise) appearing on the most recent
consolidated balance sheet of Alliant Energy Corporation as of the date of
determination, net of applicable reserves and deductions, but excluding
goodwill, trade names, trademarks, patents, unamortized debt discount and all
other like intangible assets (which term shall not be construed to include such
revaluations), less the aggregate of the consolidated current liabilities of
Alliant Energy Corporation appearing on such balance sheet.

     "Debt" is defined in the Indenture as all of our obligations evidenced by
bonds, debentures, notes or similar evidences of indebtedness in each case for
money borrowed.

     "Lien" is defined in the Indenture as any mortgage, lien, pledge, security
interest or other encumbrance. The term "Lien" does not include any easements,
rights-of-way, restrictions and other similar encumbrances and encumbrances
consisting of zoning restrictions, leases, subleases, licenses, sublicenses,
restrictions on the use of property or defects in the title thereto.

  Limitation on Sale and Lease-Back Transactions

     The Indenture provides that we will not enter into any Sale and Lease-Back
Transaction (as defined below) unless:

     -  such transaction involves a lease for a temporary period not to exceed
        three years;

     -  such transaction is between us and one of our affiliates;

     -  we would be entitled to incur Debt secured by a Lien on the assets or
        property involved in the Sale and Lease-Back Transaction at least equal
        to the Attributable Debt (as defined below) with respect to the Sale and
        Lease-Back Transaction, without equally and ratably securing the senior
        notes, as described under "-- Limitation on Liens" above, other than as
        described in the second paragraph of that description;

     -  we enter into the Sale and Lease-Back Transaction within 270 days after
        our initial acquisition of the assets or property subject to the Sale
        and Lease-Back Transaction;

     -  the aggregate amount of all Attributable Debt with respect to all Sale
        and Lease-Back Transactions then in effect does not exceed 10% of
        Alliant Energy Corporation's Consolidated Net Tangible Assets; or

     -  within 12 months preceding the sale or transfer or 12 months following
        the sale or transfer, regardless of whether we make any such sale or
        transfer, we apply, in the case of a sale or transfer for cash, an
        amount equal to the net proceeds of the sale or transfer and, in the
        case of a sale or transfer other than for cash, an amount equal to the
        fair value of the assets so leased at the time that we enter into such
        arrangement (as determined by our Board of Directors), (a) to the
        retirement of Debt, incurred or assumed by us which by its terms matures
        at, or is extendible or renewable at the option of the obligor to, a
        date more than 12 months after the date of incurring, assuming or
        guaranteeing such Debt or (b) to an investment in any of our assets.

                                       34
<PAGE>   36

     "Attributable Debt" is defined in the Indenture as, with respect to any
particular Sale and Lease-Back Transaction, at the time of determination, the
present value (discounted at the rate of interest implicit in the transaction
determined in accordance with generally accepted accounting principles) of the
obligation of the lessee for net rental payments during the remaining term of
the lease included in the Sale and Lease-Back Transaction (including any period
for which such lease has been extended or may, at the option of the lessor, be
extended).

     "Sale and Lease-Back Transaction" is defined in the Indenture as any
arrangement with any entity providing for the lease by us of any of the assets
that we have sold or transferred or that we have agreed to sell or transfer to
that entity.

  Consolidation, Merger, Conveyance, Sale or Lease

     The Indenture provides that we may, without the consent of any holders of
the new senior notes, consolidate with, merge into or be merged with, or convey,
transfer or lease our property and assets substantially as an entirety to
another U.S. entity so long as:

     -  if we are not the surviving entity, the surviving entity expressly
        assumes by supplemental indenture all of our applicable obligations
        under the new senior notes and the Indenture;

     -  immediately after giving effect to the transaction, no Event of Default
        and no event which, after notice or lapse of time or both, would become
        an Event of Default, has occurred and is continuing; and

     -  either we or our successor delivers to the Trustee an officers'
        certificate and an opinion of counsel stating that such consolidation,
        merger, conveyance, transfer or lease, and if a supplemental indenture
        is required by the transaction, the supplemental indenture, comply with
        the Indenture and all conditions precedent in the Indenture relating to
        such transaction.

     In addition, we may assign and delegate all of our rights and obligations
under the Indenture, the new senior notes, the Supplemental Indenture and all
other documents, agreements and instruments related thereto, as applicable, to
Alliant Energy Corporation or a subsidiary of Alliant Energy Corporation, any
person that owns all of our capital stock or any person that owns all of the
capital stock of a person that owns all of our capital stock, and upon the
assumption of such rights and obligations by such person, we will be
automatically released from the obligations, provided that immediately after
giving effect to the transaction, no Event of Default, and no event which, after
notice or lapse of time or both, would become an Event of Default, has occurred
and is continuing.

     The Indenture also provides that Alliant Energy Corporation may, without
the consent of any holders of the new senior notes, consolidate with, merge into
or be merged with, or convey, transfer or lease its property and assets
substantially as an entirety to another U.S. entity so long as:

     -  if Alliant Energy Corporation is not the surviving entity, the surviving
        entity assumes by supplemental indenture all of Alliant Energy
        Corporation's obligations under the guarantees and the Indenture;

     -  immediately after giving effect to the transaction, no Event of Default,
        and no event which, after notice or lapse of time or both, would become
        an Event of Default, has occurred and is continuing; and

     -  either Alliant Energy Corporation or the successor person delivers to
        the Trustee an officers' certificate and an opinion of counsel stating
        that such consolidation, merger, conveyance, transfer or lease, and if a
        supplemental indenture is required by the transaction, the supplemental
        indenture, comply with the Indenture and all conditions precedent in the
        Indenture, relating to such transactions.

                                       35
<PAGE>   37

  Money For Securities Payments To Be Held In Trust

     The Indenture provides that if we at any time act as our own Paying Agent
with respect to the new senior notes, we will, on or before each due date of the
principal of, or any premium or interest on, any of the new senior notes,
segregate and hold in trust for the benefit of the persons entitled a sum in the
currency in which the new senior notes are payable sufficient to pay the
principal or any premium or interest due until such sums are paid or otherwise
disposed of, and will promptly notify the Trustee of our action or failure to
act.

     Whenever we have one or more Paying Agents for any series of debt
securities, we will, on or prior to each due date of the principal of, or any
premium or interest on any series of debt securities, deposit with any Paying
Agent a sum sufficient to pay the principal or any premium or interest due, the
sum to be held in trust for the benefit of the persons entitled, and, unless the
Paying Agent is the Trustee, we will promptly notify the Trustee of our action
or failure to act.

     We will cause each Paying Agent for each series of debt securities, if
other than the Trustee, to execute and deliver to the Trustee an agreement that
requires the Paying Agent:

     -  to hold all sums held by it for the payment of the principal of, or any
        premium or interest on, any series of debt securities in trust for the
        benefit of the persons entitled until such sums are paid or otherwise
        disposed of as provided in the Indenture;

     -  to give the Trustee notice of any default by us or Alliant Energy
        Corporation in the making of any payment of principal, any premium or
        interest on any series of debt securities; and

     -  at any time during the continuance of the default, upon the written
        request of the Trustee, pay to the Trustee all sums held in trust by it.

     We or Alliant Energy Corporation may at any time pay, or direct any Paying
Agent to pay, to the Trustee all sums held in trust by us or the Paying Agent,
and such sums will be held by the Trustee upon the same terms as those
applicable to us or the Paying Agent; and, upon such payment by the Paying Agent
to the Trustee, the Paying Agent will be released from all further liability
with respect to such sums.

     Except as otherwise provided in the Indenture, any money deposited with the
Trustee or the Paying Agent, or held by us, in trust for the payment of the
principal of, any premium or interest on any series of debt securities and
remaining unclaimed for two years after such principal or any such premium or
interest has become due and payable will be discharged from such trust; and the
holder of the new senior note will thereafter, as an unsecured general creditor,
look only to us or Alliant Energy Corporation, as the case may be, for payment,
and all liability of the Trustee or the Paying Agent with respect to the trust
money, and all liability of us as trustee thereof, will cease; provided,
however, that the Trustee or the Paying Agent may at our expense cause to be
published once, in an authorized newspaper or mailed to holders of the new
senior notes, or both, notice that such money remains unclaimed and that, after
a date specified, which will not be less than 30 days from the date of the
publication or mailing nor later than two years after the principal and any
premium or interest have become due and payable, any unclaimed balance of such
money then remaining will be repaid to us or Alliant Energy Corporation, as the
case may be.

  Company And Guarantor Statements As To Compliance; Notice Of Certain Defaults

     We and Alliant Energy Corporation will each deliver to the Trustee, within
120 days after the end of each fiscal year, a written statement signed by our
respective principal executive officer, principal financial officer or principal
accounting officer, stating that:

     -  a review of our respective activities during the year and of our
        respective performances under the Indenture has been made under such
        officer's supervision, and

     -  to the best of such officer's knowledge, based on that review, (a) we or
        Alliant Energy Corporation, as the case may be, have complied with all
        the conditions and covenants imposed on

                                       36
<PAGE>   38

        each of us by the Indenture throughout the year, or, if there has been a
        default in the fulfillment of any condition or covenant, specifying each
        default known to such officer and its nature and status, and (b) no
        event has occurred and is continuing which is, or after notice or lapse
        of time or both would become, an Event of Default, or, if such an event
        has occurred and is continuing, specifying each such event known to such
        officer and its nature and status.

     We and Alliant Energy Corporation will deliver to the Trustee, within five
days after its occurrence, written notice of any Event of Default or any event
which after notice or lapse of time or both would become an Event of Default.

MODIFICATION OF THE INDENTURE

     We, Alliant Energy Corporation and the Trustee may modify and amend the
Indenture or any supplemental indenture or the rights of the holders of the debt
securities of each series to be affected with the consent of the holders of more
than 50% of the principal amount of the outstanding debt securities of each
affected series (with each series voting as a class). Such majority holders may
also waive compliance by us or Alliant Energy Corporation with any provision of
the Indenture, any supplemental indenture or the debt securities of any series.
However, without the consent of a holder of each debt security affected, an
amendment or waiver may not:

     -  reduce the amount of debt securities whose holders must consent to an
        amendment or waiver;

     -  change the rate or the time for payment of interest;

     -  change the principal or the fixed maturity;

     -  waive a default in the payment of principal, premium or interest;

     -  make any debt securities payable in a different currency;

     -  make any change in the provisions of the Indenture concerning (a) waiver
        of existing defaults; (b) right of holders of debt securities to receive
        payment; or (c) amendments and waivers with consent of holders of debt
        securities;

     -  impair the right to institute suit for the enforcement of any payment on
        or after the stated maturity of such payment or, in the case of
        redemption, on or after the redemption date; or

     -  modify or effect in any manner adverse to the holders the terms and
        conditions of Alliant Energy Corporation's obligations regarding due and
        punctual payment of principal of, or any premium or interest on, or any
        sinking fund requirements of, any debt securities subject to guarantees.

     We, Alliant Energy Corporation and the Trustee may amend or supplement the
Indenture without the consent of any holder of any of the debt securities:

     -  to cure any ambiguity, defect or inconsistency in the Indenture, any
        supplemental indenture, the debt securities or guarantees;

     -  to provide for the assumption of all of our obligations under the debt
        securities, the Indenture, or any supplemental indenture or of Alliant
        Energy Corporation's obligations under the guarantees and the Indenture
        or any supplemental indenture by any corporation in connection with a
        merger or consolidation of us or Alliant Energy Corporation or transfer
        or lease of our property and assets substantially as an entirety or
        Alliant Energy Corporation's property and assets substantially as an
        entirety;

     -  make any change that does not adversely affect the rights of any holder
        of debt securities;

     -  to add to the rights of holders of any of the debt securities;

     -  to secure any debt securities as provided under the heading "--
        Limitation on Liens";

                                       37
<PAGE>   39

     -  to evidence the succession of another person to us or Alliant Energy
        Corporation, and the assumption by the successor person of the covenants
        of us and Alliant Energy Corporation, as the case may be, provided in
        the Indenture or the senior notes;

     -  to establish the form or terms of any debt securities;

     -  to evidence and provide for the acceptance of appointment under the
        Indenture by a successor Trustee with respect to the debt securities and
        to add to or change any of the provisions of the Indenture necessary to
        facilitate the administration of the Indenture by more than one Trustee;
        or

     -  to supplement any of the provisions of the Indenture to the extent
        necessary to permit or facilitate defeasance (as defined below) and
        discharge of any debt securities, provided that such action will not
        adversely affect the interests of any holder of any debt security in any
        material respect.

EVENTS OF DEFAULT

     Any one of the following is an Event of Default with respect to the senior
notes:

          (a) if we or Alliant Energy Corporation default in the payment of any
     interest on the senior notes, and such default continues for 30 days;

          (b) if we or Alliant Energy Corporation default in payment of
     principal of or premium, if any, on the senior notes when the same become
     due at maturity, upon redemption, by declaration or otherwise;

          (c) if we or Alliant Energy Corporation materially default in the
     performance or materially breach any of our respective covenants or
     obligations in the Indenture, any supplemental indenture or the senior
     notes and this material default or breach continues for a period of 90 days
     after we or Alliant Energy Corporation receive written notice from the
     Trustee or the holders of at least 25% in aggregate principal amount of the
     outstanding senior notes;

          (d) if we or Alliant Energy Corporation default in the payment of the
     principal of any bond, debenture, note or other evidence of indebtedness,
     in each case for money borrowed, or in the payment of principal under any
     mortgage, indenture or instrument under which there may be issued or by
     which there may be secured or evidenced any indebtedness for money
     borrowed, which default for payment of principal is in an aggregate
     principal amount exceeding $25,000,000 (or its equivalent in any other
     currency or currencies) when such indebtedness becomes due and payable
     (whether at maturity, upon redemption or acceleration or otherwise), if
     such default continues unremedied or unwaived for more than 30 business
     days and the time for payment of such amount has not been expressly
     extended;

          (e) our failure or the failure by Alliant Energy Corporation generally
     to pay our respective debts as they become due, or the admission in writing
     of our inability or Alliant Energy Corporation's inability to pay our
     respective debts generally, or the making of a general assignment for the
     benefit of our respective creditors, or the institution of any proceeding
     by or against Alliant Energy Corporation or us (other than any proceeding
     brought against us or Alliant Energy Corporation, as applicable, that is
     dismissed within 180 days from its commencement) seeking to adjudicate us
     or Alliant Energy Corporation, as the case may be, bankrupt or insolvent,
     or seeking liquidation, winding up, reorganization, arrangement,
     adjustment, protection, relief or composition (in each case, other than a
     solvent liquidation, winding up, reorganization, arrangement, adjustment,
     protection, relief or composition) of us or Alliant Energy Corporation, as
     the case may be, or our respective debts under any law relating to
     bankruptcy, insolvency, reorganization, moratorium or relief of debtors, or
     seeking the entry of an order for relief or appointment of an
     administrator, receiver, trustee, intervenor or other similar official for
     us or Alliant Energy Corporation, as the case may be, or for any
     substantial part of our property or the property of Alliant Energy
     Corporation, or the taking of any action by Alliant Energy Corporation or
     us to authorize any of the actions set forth in this clause; and

                                       38
<PAGE>   40

          (f) a material default in the performance or material breach by
     Alliant Energy Corporation of any covenant or obligation of Alliant Energy
     Corporation contained in the guarantee, and the continuance of such
     material default or breach for a period of 90 days after which we or
     Alliant Energy Corporation receive written notice from the Trustee or the
     holders of at least 25% in aggregate principal amount of the senior notes.

     If an Event of Default with respect to the senior notes occurs and is
continuing, either the Trustee or the holders of at least 25% in aggregate
principal amount of the outstanding senior notes may declare the principal
amount of the outstanding senior notes, and any interest accrued on the senior
notes, to be due and payable immediately by delivering a written notice to us
and Alliant Energy Corporation (and to the Trustee if given by the holders). At
any time after this declaration of acceleration has been made, but before a
judgment or decree for payment of money has been obtained, the holders of a
majority in principal amount of all of the senior notes, by notice to the
trustee, may rescind this declaration and all its consequences if all Events of
Default have been cured or waived (other than the non-payment of principal of
the outstanding new senior notes which has become due solely by reason of the
declaration of acceleration), and such declaration of acceleration and its
consequences will be automatically annulled and rescinded.

     Holders of the new senior notes may not enforce the Indenture, the new
senior notes or any guarantees, if applicable, unless:

     -  the holder has previously given written notice to the Trustee of a
        continuing Event of Default with respect to the senior notes;

     -  the holders of not less than 25% in aggregate principal amount of the
        senior notes have made written request to the Trustee to institute
        proceedings in respect of such Event of Default in its own name as
        Trustee;

     -  the holder or holders have offered the Trustee indemnity satisfactory to
        the Trustee against the costs, expenses and liabilities to be incurred
        in compliance with such request;

     -  the Trustee, for 60 days after its receipt of such notice, request and
        offer of indemnity, has failed to institute any such proceedings; and

     -  no direction inconsistent with such written request has been given to
        the Trustee during the 60-day period by the holders of a majority of the
        outstanding aggregate principal amount of the senior notes.

     However, these limitations do not apply to a suit instituted by a holder of
any new senior notes for the enforcement of the payment of the principal of or
premium, if any, or interest on the new senior notes on or after the applicable
due date specified in the new senior notes.

     If the Trustee collects any money pursuant to an Event of Default, it will
pay out the money in the following order:

     -  first, to the Trustee for amounts to it as compensation for its services
        and any indemnities owed to it;

     -  second, to holders of the senior notes in respect of which or for the
        benefit of which such money has been collected for amounts due and
        unpaid on the senior notes for principal and interest, ratably, without
        preference or priority of any kind, according to the amounts due and
        payable on the senior notes for principal and interest, respectively;
        and

     -  third, to the person or persons lawfully entitled thereto, or as a court
        of competent jurisdiction may direct.

     The Trustee may fix a record date (with respect to registered securities)
and payment date for any such payment to holders of the senior notes.

                                       39
<PAGE>   41

     Any such record date will not be less than 10 days nor more than 60 days
prior to the applicable payment date.

OPTIONAL REDEMPTION

     We may redeem the new senior notes at our option in whole or in part at any
time, on at least 30 days' but not more than 60 days' prior written notice
mailed to the registered holders of the new senior notes, at a price equal to
the greater of (a) 100% of the principal amount of the new senior notes being
redeemed and (b) the sum of the present values of the principal amount of the
new senior notes to be redeemed and the remaining scheduled payments of interest
on the new senior notes from the redemption date to November 9, 2009, discounted
from their respective scheduled payment dates to the redemption date
semi-annually (assuming a 360-day year consisting of twelve 30-day months) at a
discount rate equal to the Treasury Yield plus 20 basis points, plus accrued
interest on the new senior notes to the redemption date.

     "Treasury Yield" means, with respect to any redemption date, the annual
rate equal to the semi-annual equivalent yield to maturity of the Comparable
Treasury Issue (as defined below), assuming a price for the Comparable Treasury
Issue (expressed as a percentage of its principal amount) equal to the
Comparable Treasury Price (as defined below) for such redemption date.

     "Comparable Treasury Issue" means the United States treasury security
selected by an Independent Investment Banker (as defined below) as having a
maturity comparable to the remaining term of the senior notes to be redeemed
that would be utilized, at the time of selection and in accordance with
customary financial practice, in pricing new issues of corporate debt securities
of comparable maturity to the remaining term of the senior notes.

     "Comparable Treasury Price" means, with respect to any date of redemption,
(a) the average of the bid and asked prices for the Comparable Treasury Issue
(expressed in each case as a percentage of its principal amount) on the third
business day preceding the redemption date, as set forth in the daily
statistical release (or any successor release) published by the Federal Reserve
Bank of New York and designated "Composite 3:30 p.m. Quotations for U.S.
Government Securities" or (b) if such release (or any successor release) is not
published or does not contain such prices on the business day in question, the
Reference Treasury Dealer Quotation (as defined below) for the redemption date.

     "Independent Investment Banker" means an independent investment banking
institution of national standing appointed by us and reasonably acceptable to
the Trustee.

     "Reference Treasury Dealer Quotation" means, with respect to the Reference
Treasury Dealer (as defined below) and redemption date, the average, as
determined by us, of the bid and asked prices for the Comparable Treasury Issue
(expressed in each case as a percentage of its principal amount and quoted in
writing to us by the Reference Treasury Dealer at 5:00 p.m. on the third
business day preceding the redemption date).

     "Reference Treasury Dealer" means a primary United States government
securities dealer in New York City appointed by us and reasonably acceptable to
the Trustee.

     Notice of redemption will be mailed by first class mail at least 30 but not
more than 60 days before the redemption date to each holder of the new senior
notes to be redeemed at its registered address.

     If fewer than all the new senior notes are to be redeemed, selection of new
senior notes for redemption will be made by the Trustee in any manner the
Trustee deems fair and appropriate and that complies with applicable legal and
securities exchange requirements.

     Unless we default in payment of the redemption price, from and after the
date of redemption, the new senior notes or portions thereof called for
redemption will cease to bear interest, and the holders of the new senior notes
will have no right in respect of the new senior notes except the right to
receive the redemption price.

                                       40
<PAGE>   42

DEFEASANCE AND COVENANT DEFEASANCE

     The Indenture provides that we and Alliant Energy Corporation may elect (a)
to be discharged from any and all of our respective obligations in respect of
the new senior notes ("defeasance") (except in each case for the obligations to
register the transfer or exchange of the new senior notes, replace stolen, lost
or mutilated new senior notes, maintain paying agencies and hold moneys for
payments in trust) or (b) not to comply with certain covenants ("covenant
defeasance") of the Indenture with respect to the new senior notes described
above under "-- Covenants" if, in either case, we and Alliant Energy Corporation
irrevocably deposit with the Trustee money or U.S. Government Obligations (as
defined below) or a combination of money or U.S. Government Obligations, in an
amount sufficient (together with interest paid on the U.S. Government
Obligations) to pay, when due, the principal of and premium, if any, and
interest on the outstanding new senior notes to maturity or redemption or an
installment of interest, as the case may be. We and Alliant Energy Corporation
must satisfy certain other conditions before we may effect defeasance or
covenant defeasance. These conditions include:

     -  that no Event of Default or event, which with notice or lapse of time
        would become an Event of Default (including by reason of such deposit)
        with respect to the new senior notes, will have occurred and be
        continuing on the date of the deposit or insofar as an Event of Default
        described in clause (e) of the first paragraph under "-- Events of
        Default" is concerned, at any time during the period ending on the 181st
        day of such deposit (it being understood that this condition will not be
        satisfied until the expiration of such period); and

     -  that the defeasance or covenant defeasance will not result in the breach
        or violation of, or constitute a default under, the Indenture or any
        other material agreement or instrument under which we are bound or under
        which Alliant Energy Corporation is bound, as the case may be.

     To exercise any such option, we or Alliant Energy Corporation, as
applicable, will be required to deliver to the Trustee (a) an opinion of
independent counsel of recognized standing to the effect that (1) the holders of
the new senior notes will not recognize income, gain or loss for United States
federal income tax purposes as a result of such deposit, and will be subject to
United States federal income tax on the same amounts, in the same manner and at
the same times as would have been the case absent such deposit, which in the
case of defeasance must be based on a change in law or a published ruling by the
United States Internal Revenue Service and (2) the deposit will not result in us
or Alliant Energy Corporation being deemed an "investment company" required to
be registered under the Investment Company Act of 1940 and (b) an officer's
certificate as to compliance with all conditions precedent provided for in the
Indenture relating to the satisfaction and discharge of the new senior notes.

     If we or Alliant Energy Corporation wish to deposit or cause to be
deposited money or U.S. Government Obligations to pay or discharge the principal
of, premium, if any, and interest on the outstanding new senior notes to and
including a redemption date on which all of the outstanding new senior notes are
to be redeemed, the redemption date will be irrevocably designated by a
resolution of our Board of Directors or a resolution of the Board of Directors
of Alliant Energy Corporation, as the case may be, delivered to the Trustee on
or prior to the date of deposit of such money or U.S. Government Obligations,
and such Board resolution will be accompanied by an irrevocable notice of the
defeasance to the Trustee.

     If the Trustee is unable to apply any money or U.S. Government Obligations
deposited in trust to effect a defeasance or covenant defeasance by reason of
any order or judgment of any court or governmental authority enjoining,
restraining or otherwise prohibiting such application, then any obligations from
which we or Alliant Energy Corporation had been discharged or released will be
revived and reinstated as though no such deposit of moneys in trust had
occurred, until the time that the Trustee is permitted so to apply all of the
money or U.S. Government Obligations deposited in trust.

     "U.S. Government Obligations" means direct obligations of the United States
for the payment of which its full faith and credit is pledged, or obligations of
a person controlled or supervised by and acting as an agency or instrumentality
of the United States and the payment of which is unconditionally

                                       41
<PAGE>   43

guaranteed by the United States, and will also include a depository receipt
issued by a bank or trust company as custodian with respect to any U.S.
Government Obligation or a specific payment of interest on or principal of any
U.S. Government Obligation held by a custodian for the account of a holder of a
depository receipt. However, except as required by law, a custodian is not
authorized to make any deduction from the amount payable to the holder of any
depository receipt from any amount received by the custodian in respect of the
U.S. Government Obligation or the specific payment of interest on or principal
of the U.S. Government Obligation evidenced by a depository receipt.

PAYMENT AND PAYING AGENT

     We have appointed the Trustee to act as paying agent with respect to the
new senior notes. We may at any time designate additional paying agents or
rescind the designation of any paying agents or approve a change in the office
through which any paying agent acts, except that we will be required to maintain
a paying agent in each place of payment for the new senior notes.

     All moneys paid by us to the paying agent for the payment of the principal
of, or premium, if any, or interest on, any new senior notes that remain
unclaimed at the end of two years after such principal, premium, if any, or
interest has become due and payable will be repaid to us and the holder of the
new senior notes will thereafter look only to us for payment of any such
amounts.

GOVERNING LAW

     The Indenture and the new senior notes will be governed by, and construed
in accordance with, the laws of the State of Wisconsin.

                                       42
<PAGE>   44

                UNITED STATES FEDERAL INCOME TAX CONSIDERATIONS

     THIS SUMMARY IS OF A GENERAL NATURE AND IS INCLUDED SOLELY FOR
INFORMATIONAL PURPOSES. IT IS NOT INTENDED TO BE, NOR SHOULD IT BE CONSTRUED AS
BEING, LEGAL OR TAX ADVICE. NO REPRESENTATION WITH RESPECT TO THE CONSEQUENCES
TO ANY PARTICULAR PURCHASER OF THE NEW SENIOR NOTES IS MADE. PROSPECTIVE
PURCHASERS SHOULD CONSULT THEIR OWN TAX ADVISORS WITH RESPECT TO THEIR
PARTICULAR CIRCUMSTANCES.

     The following is a summary of certain material United States federal income
tax consequences to a beneficial owner of new senior notes (a "United States
Holder") who is (a) a citizen or resident of the United States, (b) a
corporation, partnership or other entity treated as a corporation or a
partnership for United States federal income tax purposes created or organized
in or under the laws of the United States, any state thereof or the District of
Columbia, (c) an estate whose income is subject to United States federal income
tax regardless of its source, or (d) a trust if a court within the United States
is able to exercise primary supervision over the administration of the trust and
one or more United States persons have the authority to control all substantial
decisions of the trust.

     The following summary deals only with new senior notes held as capital
assets by purchasers at the issue price who are United States Holders and not
with special classes of holders, such as dealers in securities or currencies,
financial institutions, life insurance companies, tax-exempt entities, persons
holding new senior notes as a hedge against or which are hedged against currency
risks, and persons whose functional currency is not the U.S. dollar. Persons
considering the purchase of new senior notes should consult their own tax
advisors concerning these matters and as to the tax treatment under foreign,
state and local tax laws and regulations. There can be no assurance that the
Internal Revenue Service will not challenge the conclusions stated below, and no
ruling from the IRS has been or will be sought on any of the matters discussed
below.

     This summary is based upon the Internal Revenue Code of 1986, as amended,
Treasury Regulations, IRS rulings and pronouncements and judicial decisions now
in effect, all of which are subject to change at any time. Changes in this area
of law may be applied retroactively in a manner that could cause the tax
consequences to vary substantially from the consequences described below,
possibly adversely affecting a United States Holder. The authorities on which
this summary is based are subject to various interpretations, and it is
therefore possible that the federal income tax treatment of the purchase,
ownership and disposition of the new senior notes may differ from the treatment
described below.

CONSEQUENCES OF THE EXCHANGE OFFER TO EXCHANGING AND NONEXCHANGING HOLDERS

     The exchange of an existing senior note for a new senior note pursuant to
the exchange offer will not be taxable to an exchanging United States Holder for
federal income tax purposes. As a result, an exchanging United States Holder
will not recognize any gain or loss on the exchange; the holding period for the
new senior note will include the holding period for the existing senior note;
and the basis of the new senior note will be the same as the basis for the new
senior note.

     The exchange offer will result in no federal income tax consequences to a
nonexchanging United States Holder of existing senior notes.

GENERAL

     A United States Holder using the accrual method of accounting for federal
income tax purposes is required to include interest paid or accrued on the new
senior notes in ordinary income as interest accrues, while a United States
Holder using the cash receipts and disbursements method of accounting for
federal income tax purposes must include interest in ordinary income when
payments are received (or made available for receipt) by the United States
Holder.

     Although the existing senior notes were issued at a discount, such discount
is not considered to be original issue discount for tax purposes. However, the
existing senior notes provide for the payment of


                                       43
<PAGE>   45

additional amounts of interest under certain circumstances and therefore both
the existing and new senior notes are subject to the Treasury Regulations that
apply to debt instruments that provide for one or more contingent payments. For
purposes of determining whether the existing senior notes were issued with
original issue discount, we intend to take the position that the existing senior
notes did not, as of the issue date, represent contingent payment debt because
the likelihood of paying an increased rate of interest as a result of a
Registration Default was remote. Accordingly, both the existing and new senior
notes will not be considered to be issued with original issue discount. A United
States Holder may not take a contrary position unless such contrary position is
disclosed in the proper manner to the IRS. United States Holders should consult
their tax advisors regarding the tax consequences of the new senior notes being
treated as contingent payment debt.

     If the IRS successfully asserts that these contingent payments were not
remote as of the issue date, the amount and timing of the interest income that a
United States Holder is required to include in taxable income may have to be
redetermined and any gain or loss on a sale, exchange, redemption or retirement
of the new senior notes, may be recharacterized as ordinary income.

SALE, EXCHANGE, REDEMPTION OR RETIREMENT OF NEW SENIOR NOTES

     Upon the sale, exchange, redemption or retirement of a new senior note, a
United States Holder will generally recognize capital gain or loss equal to the
difference between the amount realized (not including any amounts attributable
to accrued and unpaid interest) and the United States Holder's tax basis in the
new senior note. A United States Holder's tax basis in a new senior note will
generally be its cost. Such capital gain or loss will generally be long-term
capital gain or loss if the new senior notes were held for more than one year;
otherwise, the capital gain or loss will be short-term.

ASSUMPTION OF THE NEW SENIOR NOTES

     An assumption (due to a consolidation, share exchange, merger, conveyance,
transfer or other transaction) of our obligations under the new senior notes may
be deemed for United States federal income tax purposes to be an exchange of the
new senior notes for new debt instruments resulting in the recognition of
taxable gain or loss to a United States Holder and possibly other adverse United
States tax consequences. Investors should consult their tax advisors regarding
the United States federal, state, local and foreign tax consequences of such an
assumption.

WITHHOLDING TAXES AND REPORTING REQUIREMENTS

     Interest payments and payments of principal and any premium with respect to
a new senior note will be reported to the extent required by the Code to the
United States Holders and the IRS. These amounts will ordinarily not be subject
to withholding of United States federal income tax. However, a backup
withholding tax at a rate of 31% will apply to these payments if a United States
Holder fails to properly certify to us or our agent the United States Holder's
taxpayer identification number and certain other information, or fails to report
all interest and dividends required to be reported on its federal income tax
returns, or otherwise fails to establish, in the manner prescribed by law, an
exemption from backup withholding. Any amount withheld under backup withholding
is allowable as a credit against the United States Holder's federal income tax
liability, provided such person furnishes the required information to the IRS.

     New IRS regulations will generally be applicable to payments made after
December 31, 1999. In general, these regulations do not significantly alter the
substantive withholding and information reporting requirements but unify and
clarify current procedures. Under the new regulations, special rules apply which
permit the shifting of primary responsibility for withholding to certain
financial intermediaries acting on behalf of beneficial owners. United States
Holders of new senior notes should consult with their own tax advisors regarding
the application of the backup withholding rules to their particular situation,
the availability of exemption therefrom, the procedure for obtaining such an
exemption, if available, and the impact of the new regulations with respect to
new senior notes.

                                       44
<PAGE>   46

                              PLAN OF DISTRIBUTION

     Each broker-dealer that receives new senior notes for its own account as a
result of market-making activities or other trading activities in connection
with the exchange offer must acknowledge that it will deliver a prospectus in
connection with any resale of such new senior notes. This prospectus, as it may
be amended or supplemented from time to time, may be used by a broker-dealer in
connection with resales of new senior notes received in exchange for existing
senior notes where such existing senior notes were acquired as a result of
market-making activities or other trading activities.

     We will not receive any proceeds in connection with the exchange offer or
any sale of new senior notes by broker-dealers. New senior notes received by
broker-dealers for their own account pursuant to the exchange offer may be sold
from time to time in one or more transactions in the over-the-counter market, in
negotiated transactions, through the writing of options on the new senior notes
or a combination of such methods of resale, at market prices prevailing at the
time of resale, at prices related to such prevailing market prices or negotiated
prices. Any such resale may be made directly to purchasers or to or through
brokers or dealers who may receive compensation in the form of commissions or
concessions from any such broker-dealers or the purchasers of any such new
senior notes. Any broker-dealer that resells new senior notes that were received
by it for its own account pursuant to the exchange offer and any broker-dealer
that participates in a distribution of such new senior notes may be deemed to be
an "underwriter" within the meaning of the Securities Act and any profit on any
such resale of new senior notes and any commissions or concessions received by
any such persons may be deemed to be underwriting compensation under the
Securities Act. The letter of transmittal states that by acknowledging that it
will deliver, and by delivering, a prospectus, a broker-dealer will not be
deemed to admit that it is an "underwriter" within the meaning of the Securities
Act. See "The Exchange Offer -- Resales of the New Senior Notes."

                                       45
<PAGE>   47

                                 LEGAL MATTERS

     Foley & Lardner of Milwaukee, Wisconsin will issue an opinion about certain
legal matters with respect to the new senior notes.

                                    EXPERTS

     The audited financial statements and schedules incorporated by reference in
this prospectus and elsewhere in the registration statement have been audited by
Arthur Andersen LLP, independent public accountants, as indicated in their
reports with respect thereto, and are included herein in reliance upon the
authority of said firm as experts in giving said reports.

                                       46
<PAGE>   48

--------------------------------------------------------------------------------
--------------------------------------------------------------------------------

                                  $250,000,000

                     [ALLIANT ENERGY RESOURCES, INC. LOGO]

                         ALLIANT ENERGY RESOURCES, INC.

                        NEW 7 3/8% SENIOR NOTES DUE 2009
                         UNCONDITIONALLY GUARANTEED BY

                           ALLIANT ENERGY CORPORATION

                            -----------------------
                                   PROSPECTUS
                            -----------------------

                                           , 1999

--------------------------------------------------------------------------------
--------------------------------------------------------------------------------
<PAGE>   49

                                    PART II

                     INFORMATION NOT REQUIRED IN PROSPECTUS

ITEM 20. INDEMNIFICATION OF DIRECTORS AND OFFICERS.

     Pursuant to the provisions of the Wisconsin Business Corporation Law and
Article VIII of the Registrants' Bylaws, directors and officers of the
Registrants are entitled to mandatory indemnification from the Registrants
against certain liabilities (which may include liabilities under the Securities
Act of 1933) and expenses (i) to the extent such officers or directors are
successful in the defense of a proceeding; and (ii) in proceedings in which the
director or officer is not successful in defense thereof, unless it is
determined that the director or officer breached or failed to perform his or her
duties to either Registrant and such breach or failure constituted: (a) a
willful failure to deal fairly with either Registrant or its shareholders in
connection with a matter in which the director or officer had a material
conflict of interest; (b) a violation of criminal law unless the director or
officer had a reasonable cause to believe his or her conduct was lawful or had
no reasonable cause to believe his or her conduct was unlawful; (c) a
transaction from which the director or officer derived an improper personal
profit; or (d) willful misconduct. Additionally, under the Wisconsin Business
Corporation Law, directors of the Registrants are not subject to personal
liability to the Registrants, their shareholders or any person asserting rights
on behalf thereof, for certain breaches or failures to perform any duty
resulting solely from their status as directors, except in circumstances
paralleling those outlined in (a) through (d) above.

     The indemnification provided by the Wisconsin Business Corporation Law and
the Registrants' Bylaws is not exclusive of any other rights to which a director
or officer of the Registrants may be entitled. The Registrants also carry
directors' and officers' liability insurance.

     The Registration Rights Agreement contains provisions under which the
underwriters agree to indemnify the directors and officers of the Registrants
against certain liabilities, including liabilities under the Securities Act of
1933 or to contribute to payments the directors and officers may be required to
make in respect thereof.

ITEM 21. EXHIBITS AND FINANCIAL STATEMENT SCHEDULES.

     (a) Exhibits. The exhibits listed in the accompanying Exhibit Index are
filed (except where otherwise indicated) as part of this Joint Registration
Statement.

     (b) Financial Statement Schedules. Schedule II - Valuation and Qualifying
Accounts is hereby incorporated by reference to Alliant Energy Corporation's
Annual Report on Form 10-K for the year ended December 31, 1998, as amended
(File No. 1-9894). All other schedules are omitted because they are not
applicable or not require, or because the required information is shown either
in the consolidated financial statements or in the notes thereto.

     (c) Reports, Opinions or Appraisals. Not applicable.

ITEM 22. UNDERTAKINGS.

     (a) The undersigned Registrant hereby undertakes:

          (1) To file, during any period in which offers or sales are being
     made, a post-effective amendment to this Registration Statement:

             (i) To include any prospectus required by Section 10(a)(3) of the
        Securities Act of 1933;

             (ii) To reflect in the prospectus any facts or events arising after
        the effective date of the Registration Statement (or the most recent
        post-effective amendment thereof) which, individually or in the
        aggregate, represent a fundamental change in the information set forth
        in the Registration Statement. Notwithstanding the foregoing, any
        increase or decrease in volume of securities offered (if the total
        dollar value of securities offered would not exceed that which was
        registered) and any deviation from the low or high end of the estimated
        maximum offering range

                                      II-1
<PAGE>   50

        may be reflected in the form of prospectus filed with the Commission
        pursuant to Rule 424(b) if, in the aggregate, the changes in volume and
        price represent no more than a 20% change in the maximum aggregate
        offering price set forth in the "Calculation of Registration Fee" table
        in the effective Registration Statement;

             (iii) To include any material information with respect to the plan
        of distribution not previously disclosed in the Registration Statement
        or any material change to such information in the registration
        statement.

        Provided, however, that paragraphs (a)(1)(i) and (a)(1)(ii) do not apply
        if the Registration Statement is on Form S-3 or Form S-8, and the
        information required to be included in a post-effective amendment by
        those paragraphs is contained in periodic reports filed by the
        Registrant pursuant to Section 13 or Section 15(d) of the Securities
        Exchange Act of 1934 that are incorporated by reference in the
        Registration Statement.

          (2) That, for the purpose of determining any liability under the
     Securities Act of 1933, each such post-effective amendment shall be deemed
     to be a new Registration Statement relating to the securities offered
     therein, and the offering of such securities at that time shall be deemed
     to be the initial bona fide offering thereof.

          (3) To remove from registration by means of a post-effective amendment
     any of the securities being registered which remain unsold at the
     termination of the offering.

     (b) Each of the undersigned Registrants hereby undertakes that, for
purposes of determining any liability under the Securities Act of 1933, each
filing of the Registrant's annual report pursuant to Section 13(a) or Section
15(d) of the Securities Exchange Act of 1934 that is incorporated by reference
in the Registration Statement shall be deemed to be a new Registration Statement
relating to the securities offered therein, and the offering of such securities
at that time shall be deemed to be the initial bona fide offering thereof.

     (c) Insofar as indemnification for liabilities arising under the Securities
Act of 1933 may be permitted to directors, officers and controlling persons of
the Registrants pursuant to the foregoing provisions, or otherwise, the
Registrants have been advised that in the opinion of the Securities and Exchange
Commission such indemnification is against public policy as expressed in the
Securities Act of 1933 and is, therefore, unenforceable. In the event that a
claim for indemnification against such liabilities (other than the payment by a
Registrant of expenses incurred or paid by a director, officer or controlling
person of a Registrant in the successful defense of any action, suit or
proceeding) is asserted by such director, officer or controlling person in
connection with the securities being registered, each of the Registrants will,
unless in the opinion of its counsel the matter has been settled by controlling
precedent, submit to a court of appropriate jurisdiction the question whether
such indemnification by it is against public policy as expressed in the Act and
will be governed by the final adjudication of such issue.

     (d) Each of the undersigned Registrants hereby undertakes to respond to
requests for information that is incorporated by reference into the Prospectus
pursuant to Item 4, 10(b), 11 or 13 of this form, within one business day of
receipt of such request, and to send the incorporated documents by first class
mail or other equally prompt means. This includes information contained in
documents filed subsequent to the effective date of the Registration Statement
through the date of responding to the request.

     (e) Each of the undersigned Registrants hereby undertakes to supply by
means of a post-effective amendment all information concerning a transaction,
and the company being acquired involved therein, that was not the subject of and
included in the Registration Statement when it became effective.

                                      II-2
<PAGE>   51

                                   SIGNATURES

     Pursuant to the requirements of the Securities Act of 1933, the Registrant
has duly caused this Registration Statement to be signed on its behalf by the
undersigned, thereunto duly authorized, in the City of Madison, State of
Wisconsin, on December 15, 1999.

                                          ALLIANT ENERGY RESOURCES, INC.

                                          By:   /s/ ERROLL B. DAVIS, JR.
                                            ------------------------------------
                                                    Erroll B. Davis, Jr.
                                                  Chief Executive Officer

     Pursuant to the requirements of the Securities Act of 1933, this
Registration Statement has been signed by the following persons in the
capacities and on the dates indicated.

<TABLE>
<CAPTION>
                  SIGNATURE                                    TITLE                         DATE
                  ---------                                    -----                         ----
<C>                                              <S>                                   <C>
          /s/ ERROLL B. DAVIS, JR.               Chief Executive Officer and           December 15, 1999
---------------------------------------------    Director (Principal Executive
            Erroll B. Davis, Jr.                 Officer)

            /s/ EDWARD M. GLEASON                Vice President-Treasurer and          December 15, 1999
---------------------------------------------    Corporate Secretary (Principal
              Edward M. Gleason                  Financial Officer)

             /s/ JOHN E. EBRIGHT                 Vice President-Controller             December 15, 1999
---------------------------------------------    (Principal Accounting Officer)
               John E. Ebright

                      *                          Director                              December 15, 1999
---------------------------------------------
               Alan B. Arends

                      *                          Director                              December 15, 1999
---------------------------------------------
              Rockne G. Flowers

                      *                          Director                              December 15, 1999
---------------------------------------------
               Joyce L. Hanes

                      *                          Director                              December 15, 1999
---------------------------------------------
                   Lee Liu

                      *                          Director                              December 15, 1999
---------------------------------------------
             Katharine C. Lyall

                      *                          Director                              December 15, 1999
---------------------------------------------
              Arnold M. Nemirow

                      *                          Director                              December 15, 1999
---------------------------------------------
              Milton E. Neshek

                      *                          Director                              December 15, 1999
---------------------------------------------
               Jack R. Newman
</TABLE>

                                      II-3
<PAGE>   52

<TABLE>
<CAPTION>
                  SIGNATURE                                    TITLE                         DATE
                  ---------                                    -----                         ----
<C>                                              <S>                                   <C>
                      *                          Director                              December 15, 1999
---------------------------------------------
               Judith D. Pyle

                      *                          Director                              December 15, 1999
---------------------------------------------
                Robert D. Ray

                      *                          Director                              December 15, 1999
---------------------------------------------
              Robert W. Schlutz

                      *                          Director                              December 15, 1999
---------------------------------------------
            Wayne H. Stoppelmoor

                      *                          Director                              December 15, 1999
---------------------------------------------
              Anthony R. Weiler

        *By: /s/ ERROLL B. DAVIS, JR.
   ---------------------------------------
            Erroll B. Davis, Jr.
              Attorney-in-fact
</TABLE>

                                      II-4
<PAGE>   53

                                   SIGNATURES

     Pursuant to the requirements of the Securities Act of 1933, the Registrant
has duly caused this Registration Statement to be signed on its behalf by the
undersigned, thereunto duly authorized, in the City of Madison, State of
Wisconsin, on December 15, 1999.

                                          ALLIANT ENERGY CORPORATION

                                          By:   /s/ ERROLL B. DAVIS, JR.
                                            ------------------------------------
                                                    Erroll B. Davis, Jr.
                                               President and Chief Executive
                                                           Officer

     Pursuant to the requirements of the Securities Act of 1933, this
Registration Statement has been signed by the following persons in the
capacities and on the dates indicated.

<TABLE>
<CAPTION>
                  SIGNATURE                                    TITLE                         DATE
                  ---------                                    -----                         ----
<C>                                              <S>                                   <C>
          /s/ ERROLL B. DAVIS, JR.               President and Chief Executive         December 15, 1999
---------------------------------------------    Officer and Director (Principal
            Erroll B. Davis, Jr.                 Executive Officer)

            /s/ THOMAS M. WALKER                 Executive Vice President and Chief    December 15, 1999
---------------------------------------------    Financial Officer (Principal
              Thomas M. Walker                   Financial Officer)

             /s/ JOHN E. EBRIGHT                 Vice President-Controller             December 15, 1999
---------------------------------------------    (Principal Accounting Officer)
               John E. Ebright

                      *                          Director                              December 15, 1999
---------------------------------------------
               Alan B. Arends

                      *                          Director                              December 15, 1999
---------------------------------------------
              Rockne G. Flowers

                      *                          Director                              December 15, 1999
---------------------------------------------
               Joyce L. Hanes

                      *                          Director                              December 15, 1999
---------------------------------------------
                   Lee Liu

                      *                          Director                              December 15, 1999
---------------------------------------------
             Katharine C. Lyall

                      *                          Director                              December 15, 1999
---------------------------------------------
              Arnold M. Nemirow

                      *                          Director                              December 15, 1999
---------------------------------------------
              Milton E. Neshek

                      *                          Director                              December 15, 1999
---------------------------------------------
               Jack R. Newman
</TABLE>

                                      II-5
<PAGE>   54

<TABLE>
<CAPTION>
                  SIGNATURE                                    TITLE                         DATE
                  ---------                                    -----                         ----
<C>                                              <S>                                   <C>
                      *                          Director                              December 15, 1999
---------------------------------------------
               Judith D. Pyle

                      *                          Director                              December 15, 1999
---------------------------------------------
                Robert D. Ray

                      *                          Director                              December 15, 1999
---------------------------------------------
              Robert W. Schlutz

                      *                          Director                              December 15, 1999
---------------------------------------------
            Wayne H. Stoppelmoor

                      *                          Director                              December 15, 1999
---------------------------------------------
              Anthony R. Weiler

        *By: /s/ ERROLL B. DAVIS, JR.
   ---------------------------------------
            Erroll B. Davis, Jr.
              Attorney-in-fact
</TABLE>

                                      II-6
<PAGE>   55

                                 EXHIBIT INDEX

<TABLE>
<CAPTION>
EXHIBIT
NUMBER                         DOCUMENT DESCRIPTION
-------                        --------------------
<S>        <C>
(4.1)      Indenture, dated as of November 4, 1999, among Alliant
           Energy Resources, Inc., Alliant Energy Corporation, as
           Guarantor, and Firstar Bank, N.A., as Trustee.
 (4.2)     First Supplemental Indenture, dated as of November 4, 1999,
           among Alliant Energy Resources, Inc., Alliant Energy
           Corporation, as Guarantor, and Firstar Bank, N.A., as
           Trustee.
 (4.3)     Form of New 7 3/8% Senior Notes due 2009 and related
           Guarantees.
 (4.4)     Purchase Agreement, dated as of November 4, 1999, among
           Alliant Energy Resources, Inc., Alliant Energy Corporation,
           Merrill Lynch, Pierce, Fenner & Smith Incorporated, Morgan
           Stanley & Co. Incorporated, Salomon Smith Barney Inc., ABN
           AMRO Incorporated and Barclays Capital Inc.
 (4.5)     Registration Rights Agreement, dated as of November 9, 1999,
           among Alliant Energy Resources, Inc., Alliant Energy
           Corporation, Merrill Lynch, Pierce, Fenner & Smith
           Incorporated, Morgan Stanley & Co. Incorporated, Salomon
           Smith Barney Inc., ABN AMRO Incorporated and Barclays
           Capital Inc.
 (5)       Opinion of Foley & Lardner (including consent of counsel).
(12)       Statement re computation of ratios of earnings to fixed
           charges.
(23.1)     Consent of Arthur Andersen LLP
(23.2)     Consent of Foley & Lardner (filed as part of Exhibit (5)).
(24)       Powers of attorney.
(25)       Form T-1 Statement of Eligibility and Qualification under
           the Trust Indenture Act of 1939 of Firstar Bank, N.A.
(99.1)     Form of Letter of Transmittal.
(99.2)     Form of Notice of Guaranteed Delivery.
(99.3)     Guidelines for Certification of Taxpayer Identification
           Number on Substitute Form W-9.
(99.4)     Form of Letter to Clients.
(99.5)     Form of Instructions to Registered Holder and/or DTC
           Participant from Beneficial Owners.
(99.6)     Form of Letter to Nominees.
</TABLE>

                                       E-1