Document:

<PAGE>   1

                   AMENDMENT TO REGISTRATION RIGHTS AGREEMENT

         THIS AMENDMENT TO REGISTRATION RIGHTS AGREEMENT, effective as April 13,
2000 (this "AGREEMENT"), between Innovative Gaming Corporation of America (the
"COMPANY") and __________________________ (the "INVESTOR").

         WHEREAS, the Investor has previously executed a Registration Rights
Agreement (the "INITIAL AGREEMENT") dated as of October 13, 1999, pursuant to
which the Company has agreed to provide certain registration rights to Investor;

         WHEREAS, pursuant to the Section 9 of the Initial Agreement, any
provision contained therein may be amended in writing by the Company and
investors holding a majority of the Registrable Securities and the parties
hereto have agreed to amend certain of the provisions of the Initial Agreement
in accordance with Section 9 thereof.

         NOW, THEREFORE, in consideration of the mutual covenants contained
herein, and other good and valuable consideration, the receipt and sufficiency
of which is hereby acknowledged, the parties hereto, intending to be legally
bound, hereby amend the Agreement as follows:

         1. AMENDMENT TO SECTION 2(B) OF THE INITIAL AGREEMENT. Section 2(b) of
the Agreement is hereby amended in its entirety and replaced with the provision
set forth below:

                   "2. REGISTRATION

                   (b) REGISTRATION DEFAULT. If the Registration Statement
         covering the Registrable Securities required to be filed by the Company
         pursuant to Section 2(a) is not (i) filed with the Commission within 90
         days after the Closing Date or (ii) declared effective by the
         Commission within 180 days after the Closing Date (either of which,
         without duplication, an "INITIAL DATE"), then the Company shall make
         the payments to the Initial Investor as provided in the next sentence
         as liquidated damages and not as a penalty. The amount to be paid by
         the Company to the Initial Investor shall be determined as of each
         Computation Date (as defined below), and such amount shall be equal to
         2% (the "LIQUIDATED DAMAGE RATE") of the Purchase Price (as defined in
         the Securities Purchase Agreement) from the Initial Date to the first
         Computation Date and 3.5% for each Computation Date thereafter,
         calculated on a pro rata basis to the date on which the Registration
         Statement is filed with (in the event of an Initial Date pursuant to
         clause (i) above) or declared effective by (in the event of an Initial
         Date pursuant to clause (ii) above) the Commission (the "PERIODIC
         AMOUNT").

                  At the option of the Company, the full Periodic Amount shall
         be paid by the Company to the Initial Investor within three days after
         each Computation Date either (x) by wire transfer of immediately
         available funds within three days after each Computation Date, or (y)
         through the issuance of duly and validly authorized and issued, fully
         paid and nonassessable shares of Common Stock valued at the Market
         Price (as such term is defined in the Company's Certificate of
         Designation of Series D 6% Convertible Preferred Stock), provided,
         however, that to the extent that funds are not available for the
         payment of the Periodic Amount by wire transfer of immediately
         available funds, the Periodic Amount shall be paid as provided in
         clause (y) above. The Common Stock to be issued in lieu of cash
         payments shall be registered for resale in the Registration Statement.

<PAGE>   2

                  As used in this Section 2(b), "COMPUTATION DATE" means the
         date which is 30 days after the Initial Date and, if the Registration
         Statement required to be filed by the Company pursuant to Section 2(a)
         has not theretofore been declared effective by the Commission, each
         date which is 30 days after the previous Computation Date until such
         Registration Statement is so declared effective.

                  Notwithstanding the above, if the Registration Statement
         covering the Registrable Securities required to be filed by the Company
         pursuant to Section 2(a) is not filed with the Commission by the 90th
         day after the Closing Date, the Company shall be in default of this
         Registration Rights Agreement."

                  2.       MISCELLANEOUS.

                           (a) ENTIRE AGREEMENT. This Amendment and the Initial
                  Agreement embody the entire agreement and understanding of the
                  parties hereto in respect of the subject matter contained
                  herein and therein.

                           (b) DEFINED TERMS. Except as otherwise expressly
                  provided, or unless the context otherwise requires, all
                  capitalized terms used herein have the meanings ascribed to
                  them in the Initial Agreement.

                           (c) COUNTERPARTS. This Amendment may be executed in
                  any number of counterparts, each of which shall be deemed an
                  original, but all of which shall constitute but one and the
                  same document.

         IN WITNESS WHEREOF, the parties have caused this Agreement to be duly
executed and delivered as of the date first above written.

<TABLE>
<S>                                                       <C>
                                                          INNOVATIVE GAMING CORPORATION OF AMERICA

                                                          By:
                                                             -------------------------------------
                                                               Name:  Edward G. Stevenson
                                                               Title:    Chief Executive Officer

                                                          Investor:

                                                          By:
                                                             -------------------------------------
                                                               Name:
                                                                    ------------------------------
</TABLE>

                                       2<PAGE>   1

                        FORM OF COMMON STOCK CERTIFICATE

                                                                     EXHIBIT 4.1
                     [Specimen of Common Stock Certificate]

Number                                                                  Shares

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

COMMON STOCK                                                   CUSIP 629377 10 2
PAR VALUE $.01

                                NRG ENERGY, INC.

              INCORPORATED UNDER THE LAWS OF THE STATE OF DELAWARE
       THIS CERTIFICATE IS TRANSFERABLE IN THE CITIES OF NEW YORK, NY AND
                                MINNEAPOLIS, MN

   THIS CERTIFIES THAT                                 is the owner of
             FULLY PAID AND NONASSESSABLE SHARES OF COMMON STOCK OF
NRG Energy, Inc. (hereinafter and on the back hereof called the "Corporation"),
transferable in person or by duly authorized attorney on the books of the
Corporation upon surrender of this certificate properly endorsed. This
certificate and the shares represented hereby are subject to all the terms,
conditions and limitations of the Certificate of Incorporation and all
Amendments thereto. This Certificate is not valid until countersigned by the
Transfer Agent and registered by the Registrar.

   WITNESS the facsimile seal of the Corporation and the facsimile signatures of
its duly authorized officers.

Dated:

/s/                                         /s/
President                                   Secretary

Countersigned and Registered:
Norwest Bank, N.A.
TRANSFER AGENT AND REGISTRAR

By: /s/
Authorized Signature

                            [Reverse of Certificate]

                                NRG ENERGY, INC.

   The Corporation will furnish without charge to each stockholder who so
requests the powers, designations, preferences and relative, participating,
optional or other special rights of each class of stock or series thereof and
the qualifications, limitations or restrictions of such powers, preferences
and/or rights. Any such request should be addressed to the Secretary of NRG
Energy, Inc., 1221 Nicollet Mall, Suite 700, Minneapolis, Minnesota 55403 or to
the Transfer Agent named on the face of this certificate.

   The following abbreviations, when used in the inscription on the face of this
Certificate, shall be construed as though they were written out in full
according to applicable laws or regulations:
<TABLE>
<S>                                             <C>
TEN COM--as tenants in common                   UNIF GIFT MIN ACT--      Custodian
TEN ENT--as tenants by the entireties                              (Cust)          (Minor)
                                                             Under Uniform Gifts to Minors
JT TEN--as joint tenants with right of                        Act
        survivorship and not as tenants                                    (State)
        in common
</TABLE>
     Additional abbreviations may also be used though not in the above list.
<PAGE>   2

   FOR VALUE RECEIVED, a                  hereby sell(s), assign(s) and
transfer(s) unto PLEASE INSERT SOCIAL SECURITY OR OTHER IDENTIFYING NUMBER OF
ASSIGNEE

   Please print or typewrite name and address of Assignee

Shares of the Common Stock represented by the within Certificate, and do hereby
irrevocably constitute and appoint                                 Attorney to
transfer the said stock on the books of the within-named Corporation with full
power of substitution in the premises.

Dated:
      ------------------
                               X:
                                 ---------------------------------------------
                                 NOTICE: THE SIGNATURE TO THIS ASSIGNMENT MUST
                                 CORRESPOND WITH THE NAME AS WRITTEN UPON THE
                                 FACE OF THE CERTIFICATE, IN EVERY PARTICULAR,
                                 WITHOUT ALTERATION OR ENLARGEMENT OR ANY CHANGE
                                 WHATEVER.

Signature(s)
                        Guaranteed:
                                   ---------------------------------------------
                        THE SIGNATURE(S) SHOULD BE GUARANTEED BY AN ELIGIBLE
                        GUARANTOR INSTITUTION (BANKS, STOCKBROKERS, SAVINGS AND
                        LOAN ASSOCIATIONS AND CREDIT UNIONS WITH MEMBERSHIP IN
                        AN APPROVED SIGNATURE GUARANTEE MEDALLION PROGRAM),
                        PURSUANT TO SEC RULE 17Ad-15.

                                       2

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