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                                                                EXHIBIT 10.15(b)

              FOURTH AMENDED AND RESTATED LIMITED WAIVER AGREEMENT

         THIS FOURTH AMENDED AND RESTATED LIMITED WAIVER AGREEMENT (the
"Agreement") is made and entered into effective as of the 1st day of September,
2000, by and between Software Spectrum, Inc., a Texas corporation (the
"Company") and Private Capital Management, Inc., a Florida corporation (the
"Shareholder"). Terms used but not otherwise defined herein shall have the
meanings assigned them in the Rights Agreement, as defined in such agreement as
referenced below.

                                   WITNESSETH:

         WHEREAS, the Company and Mellon Investor Services, LLC (the "Rights
Agent") (as successor to Keycorp Shareholder Services, Inc.), are parties to
that certain Rights Agreement, dated as of December 13, 1996 (the "Rights
Agreement"), which provides that, upon the event of any person or entity
becoming an "Acquiring Person" as defined therein (an "Event"), shareholders of
the Company may exercise certain Rights, defined therein to be the rights to
purchase from the Company certain shares of the preferred stock of the Company
having the rights and preferences set forth in the Statement of Designation
attached as Exhibit A to the Rights Agreement;

         WHEREAS, the Company and the Shareholder mutually agreed that it was in
the best interest of each of the Company and the Shareholder that the Company
effect a certain 1997 Stock Repurchase Plan (the "1997 Plan") pursuant to the
terms of which the Company from time to time during the operation of the 1997
Plan repurchased in the open market an amount equal to $2.5 Million, shares of
its common stock, par value $.01 (the "Common Stock") (the "1997 Plan
Repurchases");

         WHEREAS, in order to preclude the 1997 Plan Repurchases from resulting
in the Shareholder owning a percentage of the Company's stock that would result
in an Event (the "Shareholder Event"), which Shareholder Event, upon agreement
of the Company and the Shareholder, would have had undesirable consequences for
each of the Company and the Shareholder, the Company and the Shareholder
executed and delivered that certain Limited Waiver Agreement dated as of July
31, 1997 (the "Waiver Agreement");

         WHEREAS, following the completion of the 1997 Plan Repurchases, the
Company and the Shareholder mutually agreed that it was in the best interest of
each of the Company and the Shareholder that the Company effect a certain 1998
Stock Repurchase Plan (the "1998 Plan") pursuant to the terms of which the
Company from time to time during the operation of the 1998 Plan repurchased, for
an additional amount not to exceed in the aggregate $2.5 Million, in the open
market, a certain number of shares of its Common Stock (the "1998 Repurchases");

         WHEREAS, in order to preclude the 1998 Repurchases from resulting in
the Shareholder owning a percentage of the Company's Common Stock that would
result in a Shareholder Event, the Company and the Shareholder executed and
delivered that certain Amended and Restated Limited Waiver Agreement dated as of
July 7, 1998 (the "Amended Waiver Agreement");

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         WHEREAS, following completion of the 1998 Repurchases, the Company and
the Shareholder mutually agreed that it was in the best interest of each of the
Company and the Shareholder that the Company effect a certain 1999 Stock
Repurchase Plan (the "1999 Plan") pursuant to the terms of which the Company
from time to time repurchased in the open market shares of the Company's Common
Stock up to an aggregate of $5.0 million (the "1999 Repurchases").

         WHEREAS, in order to preclude the 1999 Repurchases from resulting in
the Shareholder owing a percentage of the Company's Common Stock that would
result in a Shareholder Event, the Company and the Shareholder executed and
delivered that certain Second Amended and Restated Limited Waiver Agreement
dated as of March 29, 1999 (the "Second Amended Waiver Agreement").

         WHEREAS, following completion of the 1999 Repurchases, the Company and
the Shareholder mutually agreed that it was in the best interest of each of the
Company and the Shareholder that the Company effect a certain 2000 Stock
Repurchase Plan (the "2000 Plan") pursuant to the terms of which the Company
from time to time repurchased shares of the Company Common Stock up to an
aggregate of $5.0 million (the "2000 Repurchases");

         WHEREAS, in order to preclude the 2000 Repurchases from resulting in
the Shareholder owning a percentage of the Company's Common Stock that would
result in a Shareholder Event, the Company and the Shareholder executed and
delivered that certain Third Amended and Restated Limited Waiver Agreement dated
as of December 15, 1999 (the "Third Amended Waiver Agreement");

         WHEREAS, the Company and the Shareholder have mutually agreed that it
is in the best interest of each of the Company and the Shareholder that the
Company effect certain additional stock repurchases and implement a 2001 Stock
Repurchase Plan (collectively, the "2001 Plan") pursuant to which the Company
will from time to time during operation of the 2001 Plan the repurchase an
additional amount of the Company's Common Stock not to exceed $6.8 million (the
"2001 Repurchases"); and

         WHEREAS, in order to preclude the 2001 Repurchases from resulting in
the Shareholder owning a percentage of the Company's Common Stock that would
result in a Shareholder Event, the Company and the Shareholder have mutually
agreed that it is in the best interest of each of the Company and the
Shareholder to amend and restate the terms of the Third Amended Waiver
Agreement, expressly to effect the 2001 Repurchases;

         NOW, THEREFORE, in order to facilitate the 2001 Repurchases pursuant to
the 2001 Plan and simultaneously to preclude the occurrence of the Shareholder
Event, the Company and the Shareholder, in consideration of the mutual covenants
and agreements herein contained, do hereby agree as follows:

         1.       CERTAIN DEFINITIONS.

                  "Affiliate(s)" shall mean any person or entity that directly,
         or indirectly through one or more intermediaries, controls or is
         controlled by, or is under common control with, the Shareholder.
         Furthermore, with respect to the Shareholder, "Affiliate(s)" shall also
         mean any person or entity for whom the Shareholder acts as an
         investment advisor or consultant with respect to the Company.

                                      -2-
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                  "Beneficial Ownership" shall have the meaning assigned to such
         term in Rule 13d-3 of the General Rules and Regulations under the
         Securities Exchange Act of 1934, as amended as in effect on the date
         hereof.

                  "Control" shall mean the possession, direct or indirect, of
         the power to direct or cause the direction of the management and
         policies of the Company, whether through ownership of the Common Stock,
         by contract, or otherwise.

                  "Current Shareholder Position" shall have the meaning assigned
         it in Section 2 below.

                  "Prohibited Activity" shall mean: (i) any attempt by the
         Shareholder or any of its Affiliates to gain Control of the Company;
         (ii) any Prohibited Transaction, as hereinafter defined or (iii) any
         public action on the part of the Shareholder or any of its Affiliates,
         acting individually or in concert with other persons, which could
         reasonably be construed: (a) as an attempt to effect a change of
         Control including, but not limited to, the issuance of press releases
         or the filing of documents with the Securities And Exchange Commission
         or any other Federal or State governmental entity or (b) as an action
         contrary to the position of the then current board of directors of the
         Company.

                  "Prohibited Transaction" shall mean any transaction by the
         Shareholder or any of its Affiliates which would result in the
         Beneficial Ownership by the Shareholder or any of its Affiliates,
         either individually or as a group, of the Common Stock in an amount in
         excess of the Current Shareholder Position.

                  "Standstill Period" shall mean that time period commencing on
         the date of this Agreement and ending on December 15, 2004.

         2.       REPRESENTATIONS AND WARRANTIES OF THE COMPANY AND THE
                  SHAREHOLDER.

                  A. The Company hereby represents and warrants to the
Shareholder that it (i) has duly authorized the 2001 Plan and, subject to
relevant market and other factors and conditions affecting the Company in the
good faith judgment of its Board of Directors, the Company will make bona fide
efforts, during the operation of the 2001 Plan, to effect the 2001 Repurchases
pursuant to the 2001 Plan and (ii) is currently authorized to spend up to $6.8
Million on the 2001 Repurchases pursuant to the 2001 Plan.

                  B. The Shareholder hereby represents and warrants to the
Company that, as of the date hereof, the total number of shares of Common Stock
of which the Shareholder or any of its Affiliates or Associates has Beneficial
Ownership is 861,854 shares (as such share ownership may be affected from time
to time by stock splits, stock dividends, reverse splits or any other such
matter affecting all shareholders equally, the "Current Shareholder Position").

                                      -3-
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         3.       CERTAIN COVENANTS AND AGREEMENTS.

                  A.       Covenants and Agreements of the Company.

                           a. The Company hereby agrees that, notwithstanding
the fact that the 2001 Repurchases pursuant to the 2001 Plan may result in the
Shareholder Event, if the Shareholder Event should occur solely by virtue of the
1997 Plan Repurchases, the 1998 Repurchases, the 1999 Repurchases, the 2000
Repurchases and/or the 2001 Repurchases pursuant to the 2001 Plan, such
Shareholder Event shall be deemed not to have occurred, and the Company hereby
grants a limited waiver of any provision of the Rights Agreement pursuant to the
terms of which the Shareholder Event would be considered to have occurred solely
by virtue of the 1997 Plan Repurchases, the 1998 Repurchases, the 1999
Repurchases, the 2000 Repurchases and/or the 2001 Repurchases.

                           b. The Company hereby acknowledges and agrees that,
by virtue of the operation of this Agreement, the Shareholder, alone or together
with its Affiliates and Associates, may have Beneficial Ownership of twenty
percent (20%) or more of the shares of Common Stock of the Company then
outstanding, provided that such circumstance occurs solely as a result of the
1997 Plan Repurchases, the 1998 Repurchases Repurchases, the 1999 Repurchases,
the 2000 Repurchases and/or the 2001 Repurchases, and yet not be deemed to be an
"Acquiring Person" for purposes of the Rights Agreement.

                           c. The Company acknowledges and agrees that nothing
in this Agreement shall preclude the Shareholder from (i) effecting sales and
purchases of the Common Stock so long as the Current Shareholder Position is not
exceeded or (ii) subject to the provisions of paragraph 3(B)(a) below,
exercising the voting privileges commensurate with its ownership of the Common
Stock.

                  B.       Covenants and Agreements of the Shareholder.

                           a. The Shareholder agrees that neither the
Shareholder nor any of its Affiliates shall engage in any Prohibited Activity
(i) at any time that the Shareholder, alone or together with its Affiliates has
Beneficial Ownership of 20% or more of the outstanding Common Stock of the
Company as a result of Repurchases pursuant to any of the repurchase Plans, or
(ii) during the Standstill Period.

                           b. The Shareholder acknowledges and agrees that this
Agreement constitutes only a limited waiver of the Rights Agreement and that the
waiver herein contained applies only to the occurrence of the Shareholder Event
as the result solely of the 1997 Plan Repurchases, the 1998 Repurchases, the
1999 Repurchases, the 2000 Repurchases and/or the 2001 Repurchases and not to
any other circumstances or conditions which may result in the occurrence of the
Shareholder Event.

                           c. The Shareholder hereby further acknowledges that,
should the Shareholder Event occur as a result of or in connection with the
purchase or acquisition by the Shareholder of Common Stock of the Company which
results in an increase in the Current Shareholder Position, then this limited
waiver shall not apply and the Shareholder shall, in accordance with the terms
of the Rights Agreement, be deemed to be an "Acquiring Person."

                                      -4-
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                  C.       Covenants and Agreements of the Company and the
                           Shareholder.

                           The Company and the Shareholder acknowledge and agree
that this Agreement constitutes a limited waiver of the Rights Agreement; by
agreeing to this waiver, the Company has not agreed to waive any other
provisions of the Rights Agreement and the Company hereby expressly reserves its
right fully to enforce the Rights Agreement except as such enforcement may be
limited by the express terms of this Agreement.

         4.       GENERAL PROVISIONS.

                  A. Voidability. This Agreement shall become null and void if
the Company shall not have publicly announced its authorization of the 2001 Plan
on or before December 31, 2000.

                  B. Entire Agreement. This Agreement constitutes the entire
agreement by and among the parties with respect to the subject matter hereof.

                  C. Counterparts. This Agreement may be executed in one or more
counterparts, each of which shall be deemed an original, but all of which
together shall constitute one and the same instrument.

                  D. Assignability. This Agreement shall be binding upon and
inure to the benefit of the successors and assigns of the parties hereto;
provided, that neither this Agreement nor any right hereunder shall be
assignable by the Shareholder without the prior written consent of the Company
and the Rights Agent, but this Agreement shall be assignable by the Company to
any successor by merger or otherwise to the Company and by the Rights Agent to
any successor without the consent of the Shareholder.

                  E. Governing Law. The validity, interpretation and effect of
this Agreement shall be governed exclusively by the laws of the State of Texas.

         IN WITNESS WHEREOF, the parties hereto have executed this Agreement as
of the date first above written.

                                         SOFTWARE SPECTRUM, INC.

                                         By:    /s/ Judy Odom
                                                --------------------------------
                                         Name:
                                                --------------------------------
                                         Title: CEO
                                                --------------------------------

                                         PRIVATE CAPITAL MANAGEMENT, INC.

                                         By:    /s/ Gregg Powers
                                                --------------------------------
                                         Name:
                                                --------------------------------
                                         Title: President
                                                --------------------------------

                                      -5-

<PAGE>   6

                         ACKNOWLEDGED AND ACCEPTED:

                         MELLON INVESTOR SERVICES LLC

                         By:      /s/ Deodatt Lakeram
                                  ----------------------------------------------
                         Name:    Deodatt Lakeram
                                  ----------------------------------------------
                         Title:   Assistant Vice President, Relationship Manager
                                  ----------------------------------------------

                                      -6-<PAGE>   1
                                                                     EXHIBIT 4.4

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                                        M
                                         D
                                          C

                            MEWBOURNE ENERGY PARTNERS
                                    -A, L.P.

                         A Delaware limited partnership

Certificate Number                          Number of Limited Partner Interests

                              This Certifies That

is a Limited Partner of Mewbourne Energy Partners -A , L.P., a Delaware limited
partnership (the "Partnership"), owning the number of Limited Partner Interests
in the Partnership above specified, each Limited Partner Interest having an
initial purchase price from the Partnership of One Thousand Dollars ($1,000.00).
Each Limited Partner Interest is subject to all of the terms and conditions of
the Agreement of Partnership of the Partnership and entitled to all the rights
and privileges stated therein. This Certificate is intended solely to provide in
concise form certain information about the ownership of Limited Partner
Interests in the Partnership. All rights, obligations and other attributes
(including those relating to assignment and transfer) pertaining to the Limited
Partner Interests described in this Certificate are set forth in and governed by
the Agreement of Partnership of the Partnership, to which reference must be made
for description of such rights, obligations and other attributes. This
Certificate is not valid unless executed by an authorized officer of the
Managing Partner of the Partnership.

                                       MEWBOURNE ENERGY PARTNERS,      -A, L.P.

                                       By:   Mewbourne Development Corporation,
                                             Managing Partner

Dated:                                 BY:
                                             ----------------------------------
                                             J. Roe Buckley, Treasurer
================================================================================
<PAGE>   2

         This Certificate and the Agreement of Partnership of the Partnership
are your evidence of ownership of Limited Partner Interests, and both should be
retained. This Certificate should be submitted to the Partnership in the event
of any proposed change in ownership of your Limited Partner Interests.

         For transfer purposes, please return this Certificate to Mewbourne
Development Corporation, Investor Services Department, 3901 S. Broadway, Tyler,
Texas 75701, (903) 561-2900.

For Value received, the undersigned hereby sells, assigns and transfers
_________________ of the Limited Partner Interests represented by this
Certificate unto:

             -----------------------------------------------------
                           (Print Name of Transferee)

             -----------------------------------------------------
                         (Street Address of Transferee)

             -----------------------------------------------------
             (City)                  (State)                (Zip)

and does hereby irrevocably constitute and appoint the Managing Partner attorney
to transfer the said Limited Partner Interests on the books of the Partnership
with full power of substitution.

Subject to the terms of Section 8.1 of the Agreement of Partnership of the
Partnership, the undersigned consents/does not consent to the above-named
transferee's becoming a substituted Limited Partner in the Partnership.

Date:
      -----------------------

   ----------------------------------------------------------------------------
   (Signature* of Limited Partner Interest Holder or Authorized Representative)

   ----------------------------------------------------------------------------
              (Signature* of Joint Limited Partner Interest Holder)

   ----------------------------------------------------------------------------
               (Printed Name of Limited Partner Interest Holder)

   ----------------------------------------------------------------------------
             (Printed Name of Joint Limited Partner Interest Holder)

Signed in presence of:
                      ---------------------------------------------------------
                                         (Witness)

*NOTE: Please sign your name exactly as it is shown on the Certificate. When
Limited Partner Interests are held by joint tenants, both should sign. When
signing as attorney, executor, administrator, trustee, or guardian, please give
full title as such. If a corporation, please sign in full corporate name by an
authorized corporate officer, and indicate corporate office held by person
signing. If a partnership, please sign in partnership name by authorized person.

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