Document:

<PAGE>   1
                                                                  Exhibit 10.52

                   AMENDMENT NO. 2 TO STOCK TRANSFER AGREEMENT

     THIS AMENDMENT NO. 2 TO STOCK TRANSFER AGREEMENT entered into as of the 29
day of March, 2001, by and among AVIRON, a Delaware corporation ("Company") and
the REGENTS OF THE UNIVERSITY OF MICHIGAN ("University").

                                    RECITALS

     WHEREAS, the Company and the University are parties to that certain
Materials Transfer and Intellectual Property Agreement dated February 24, 1995
and that certain Stock Transfer Agreement dated February 24, 1995, as amended by
Amendment No. 1 to Stock Transfer Agreement, dated February 16, 2000 (the
"Transfer Agreement").

     WHEREAS, pursuant to Section 5 of the Transfer Agreement, Aviron agreed to
deliver to the University a warrant for the purchase of Aviron Common Stock
equal to one and twenty-five one-hundredths percent (1.25%) of the total number
of issued and outstanding shares of the Company's Common Stock on the Issue Date
(as defined therein).

     WHEREAS, the parties amended the Transfer Agreement to allow for the
issuance of a warrant as of February, 2000 and amended the calculation of the
number of shares to be issued pursuant to the further warrant to be issued to
the University on the Issue Date as defined therein.

     WHEREAS, the parties now desire to amend the Transfer Agreement for a
second time, in order to issue a warrant as of the date hereof and further amend
the calculation of the number of shares to be issued pursuant to the University
on the Issue Date as set forth below.

     NOW, THEREFORE, in consideration of the promises and for other good and
valuable consideration, the receipt and sufficiency of which are hereby
acknowledged, the parties agree as follows:

SECTION 1. ISSUANCE OF WARRANT.

     1.1  Promptly upon execution of this Agreement, the Company will issue to
University a warrant to purchase fifty thousand (50,000) shares of the Company
Common Stock at an exercise price per share of Ten Dollars ($10.00) (the
"Initial Exercise Price" and the "Second Warrant"). The Second Warrant shall be
in substantially the form as the warrant issued to University in February 2000
pursuant to the Transfer Agreement.

     1.2  The Company represents and warrants that the Initial Exercise Price is
properly calculated according to Section 5.3 of the Transfer Agreement.

<PAGE>   2

     1.3  In the event that the calculation of the Warrant Shares (as defined in
the Transfer Agreement and as amended below), is negative or zero, then
University shall retain the Second Warrant and there shall be no adjustment of
the number of shares exercisable under the Second Warrant.

     1.4  If University exercises/converts the New Warrant and Second Warrant in
full or portion prior to the date of the First Commercial Sale of any Product
(as defined in the Transfer Agreement) and is not able to sell the Warrant
Shares pursuant to Rule 144 under the Securities Act of 1933, as amended, then
the Company agrees to apply for registration of the Warrant Shares (this
agreement is for one such registration) for resale on a Form S-3 Registration
Statement (if such form is available for use by the Company) with the Securities
and Exchange Commission and both parties agree that such registration shall be
on terms and conditions substantially similar to those registration rights
granted to American Home Products Corporation pursuant to Section 5 of that
certain Common Stock Purchase Agreement by and between American Home Products
Corporation and the Company dated February 3, 2000.

SECTION 2. AMENDMENT OF CALCULATION FOR FURTHER ISSUANCE OF WARRANT.

     2.1  The first-paragraph of Section 5.2 of the Transfer Agreement is
further amended in its entirety as follows:

     "Subject to the provisions of Section 5.4 below, the Warrant shall be
     exercisable for a number of shares of the Company Common Stock (the
     "Warrant Shares") equal to one and twenty-five one-hundredths percent
     (1.25%) of the total number of issued and outstanding shares of the Company
     Common Stock on the Issue Date (including, on an as-converted basis,
     outstanding shares of Preferred Stock of the Company) less three hundred
     ninety thousand (390,000) shares of the Company Common Stock (as adjusted
     for recapitalizations, stock splits, dividends and the like). If such
     number is negative or zero, then no Warrant shall be issued. For purposes
     of calculating this percentage, "issued and outstanding shares of the
     Company Common Stock" shall NOT include shares of the Company Common Stock,
     or securities convertible into the Company Common Stock:"

     In Witness Whereof, the parties hereto have executed this AMENDMENT NO. 2
TO STOCK TRANSFER AGREEMENT as of the date set forth in the first paragraph
hereof.

AVIRON                                 THE REGENTS OF THE
                                       UNIVERSITY OF MICHIGAN

By:    /s/ Fred Kurland                By: /s/ Norman G. Herbert
     --------------------------            --------------------------
                                           Norman G. Herbert
                                           Associate Vice President & Treasurer

                                       By: /s/ L. Erik Lundberg
                                           --------------------------
                                           L. Erik Lundberg, CFA
                                           Chief Investment Officer

                                       2ex10-1

EXHIBIT 10.1

EXTENSION TO PROMISSORY NOTE

  	 	 	 	 	 
	
        $400,000.00

      		
        
           San Diego, San Diego County,

            California 

        

      		
        March 31,
          2001

      

FOR VALUE RECEIVED, the undersigned, L. Donald Speer, II and Kelly Elizabeth
Speer, (“Makers”), and Venture Catalyst Incorporated, a Utah corporation or its
assigns (“Holder”) hereby enter into this extension (“Extension”) to that
certain advance promissory note (“Note”), dated September 1, 2000, as follows:

RECITALS

A. In accordance with the Section 1 of the Note, the principal amount of the
Note and all unpaid interest, if any, are due and payable in full on March 31,
2001.

B. Holder has determined that it is in its best interest to extend the Note for
an additional six months, the unpaid principal amount and all accrued but
unpaid interest, if any, thereby due and payable in full on September 30, 2001.

C. As of March 31, 2001, the aggregate unpaid principal and accrued but unpaid
interest on the Note were $38,814.95.

AGREEMENT

      NOW, THEREFORE, in consideration of the premises and agreements contained
herein and other good and valuable consideration, the sufficiency and receipt
of which are hereby acknowledged, and intending to be legally bound, the Makers
and Holder hereby agree as follows:

      1. Capitalized Terms. Capitalized terms used herein shall have the same
meanings ascribed to such terms in the Note unless otherwise defined herein.

      2. Payment. Section 1(a) of the Note is hereby amended to extend the date
of Mandatory payment from March 31, 2001 to September 30, 2001.

      3. Incorporation by Reference. The parties hereto incorporate by
reference herein each and every covenant, term and condition contained in the
Note as if more fully set forth herein, subject only to the amendment and
modifications contained in this Extension, the same which shall supercede any
term or condition set forth in the Note that may be in conflict herewith.

      4. Incorporation. This Extension shall be deemed a part of and
incorporated into the Note and is hereby ratified, approved and confirmed in
each and every respect. All references to the Note or this Extension in any
other document, instrument, agreement or writing shall hereafter be deemed to
refer to the Note as modified hereby.

1

      5. Successor and Assigns. This Extension shall be binding upon Borrower,
her successors and assigns, and shall inure to the benefit of Lender, its
successor and assigns.

      6. Applicable Law. THIS EXTENSION SHALL BE GOVERNED BY, AND CONSTRUED AND
ENFORCED IN ACCORDANCE WITH, THE LAWS OFA THE STATE OF CALIFORNIA, WIHTOUT
GIVING NOTICE TO THE PRINCIPLES OF CONFLICT OF LAWS OR THE STATE OF CALIFORNIA.
THIS FIRST EXTENSION MAY BE ENFORCED IN SAN DIEGO COUNTY SUPERIOR COURT BY
AGREEMENT OF THE PARTIES HERETO.

      IN WITNESS WHEREOF, the parties have executed this Extension as of the
date first set forth above.

  	 	 	 
	Venture Catalyst Incorporated,	 	Makers
	a Utah corporation		 
	 		 
	 By: /s/ KEVIN MCINTOSH
        

        Kevin McIntosh,

        Chief Financial Officer 		 /s/ L. DONALD SPEER, II
        

        L. Donald Speer, II

      

  	 	/s/ KELLY ELIZABETH SPEER

        Kelly Elizabeth Speer 
	 	 

   

2<PAGE>   1
                                                                   EXHIBIT 10.23

               THIRD AMENDMENT TO AMENDED AND RESTATED WAREHOUSING
                         CREDIT AND SECURITY AGREEMENT

      This Third Amendment to the Amended and Restated Warehousing Credit and
Security Agreement (this "Amendment"), is entered into effective as of the 30th
day of April, 2001 by and among MORTGAGE PORTFOLIO SERVICES, INC., a Delaware
corporation ("Company"), NAB ASSET CORPORATION ("Guarantor"), WASHINGTON MUTUAL
BANK, FA, a federal association, successor by merger to BANK UNITED, in its
capacity as one of the Lenders and Administrative Agent and Collateral Agent for
the Lenders ("Agent"), the lenders party to the Warehouse Agreement, as defined
below ("Lenders"), CENTEX FINANCIAL SERVICES, INC., a Nevada corporation
("Centex"), and CENTEX CORPORATION, a Nevada corporation.

      Section 1. Recitals. Company, Agent, and Lenders have entered into that
certain Amended and Restated Warehousing Credit and Security Agreement dated
August 28, 2000 (as amended on October 15, 2000 and November 13, 2000, the
"Warehouse Agreement") for the purposes and consideration therein expressed,
pursuant to which Lenders have agreed to make loans to Company as therein
provided. Company, Guarantor, Centex, Centex Corporation, Agent, and Lenders
desire to amend the Warehouse Agreement to extend the Termination Date of the
Commitment and make such other modifications as more particularly set forth
herein. Therefore, Company, Guarantor, Centex, Centex Corporation, Agent, and
Lenders hereby agree as follows, intending to be legally bound:

      Section 2. Definitions and References. Unless the context otherwise
requires or unless otherwise expressly defined herein, the terms in the
Warehouse Agreement shall have the same meanings whenever used in this
Amendment.

      Section 3. Amendments. The Warehouse Agreement is hereby amended, as
follows:

            (a) The following definitions are hereby added to Section 1.1 of the
      Warehouse Agreement:

            "'Centex' shall mean Centex Financial Services, Inc., a Nevada
      corporation."

            "'Defective Collateral' means any Collateral that is not or ceases
      to be an Eligible Mortgage Loan, an Eligible Construction Mortgage Loan,
      an Eligible Past Due Loan, an Eligible Delinquent Loan, an Eligible
      Foreclosure Mortgage Loan, an Eligible Repurchased Mortgage Loan, or an
      Eligible REO."

            "'Stock Purchase Agreement' means the Stock Purchase Agreement dated
      as of March 16, 2001 between Centex, Stanwich Financial Services Corp.,
      and NAB Asset Corporation, as amended."

      (b) The following definition in Section 1.1 of the Warehouse Agreement is
hereby amended as follows:

<PAGE>   2

            "'Termination Date' shall mean the earlier to occur of (i) August
      31, 2001, or (ii) the date which is two (2) Business Days following the
      Administrative Agent's receipt of Notice from Centex that the Stock
      Purchase Agreement has terminated or will terminate or (iii) such earlier
      date upon which Lenders' obligation to fund shall be terminated pursuant
      to the terms of this Agreement."

      (c) The following Section 2.5(a) of the Warehouse Agreement is hereby
restated as follows:

            "The outstanding unpaid principal amount of all Advances shall be
      payable in full on the date that is sixty (60) days following the
      Termination Date."

      (d) The following section is hereby added to the end of Article 6
Affirmative Covenants. of the Warehouse Agreement for all purposes:

            "6.15 Mandatory Payment by Centex. If the Company fails to pay to
      the Administrative Agent at any time and from time to time (i) all
      outstanding Advances against any Defective Collateral plus any accrued and
      unpaid interest thereon in accordance with this Agreement, (ii) the entire
      outstanding principal amount of all Advances plus all accrued and unpaid
      interest thereon in full on the date that is sixty (60) days following the
      Termination Date and/or (iii) all accrued and unpaid fees due and payable
      to the Administrative Agent or the Lenders pursuant to Section 2.8 of this
      Agreement (all of the unpaid amounts described in (i), (ii), and (iii) are
      hereinafter collectively called the "Past Due Amounts"), Centex shall,
      absolutely and unconditionally, pay to Administrative Agent, for the
      benefit of the Lenders, all such Past Due Amounts in immediately available
      funds within five (5) Business Days after receiving Notice (which shall be
      sent by facsimile and confirmed by mail) from Administrative Agent of such
      failure; provided, however, that Centex shall not be liable for the
      repayment of any Advances made by Administrative Agent or the Lenders to
      Company after the Termination Date and all accrued and unpaid interest on
      such Advances (without implying any obligation to make Advances after the
      Termination Date) or any fees payable pursuant to Section 2.8 of this
      Agreement accruing after the Termination Date. Administrative Agent shall
      provide in its Notice to Centex a description in reasonable detail of the
      Past Due Amounts together with a list of all Pledged Mortgages
      specifically relating to such Past Due Amounts (including Pledged
      Mortgages in respect of which Wet Advances have been made) and the Past
      Due Amount owed against each Pledged Mortgage; such list shall be
      substantially in the form of EXHIBIT "T" hereto. With respect to Past Due
      Amounts relating to Defective Collateral, Administrative Agent's Notice
      shall describe the defects that have resulted in such Collateral becoming
      Defective Collateral."

      (e) Section 7.5 of the Warehouse Agreement is hereby restated as follows:

            "7.5. Minimum Consolidated Tangible Net Worth Ratio. Permit the
      ratio of Debt to Company's Consolidated Tangible Net Worth to exceed 15:1,
      computed as of the end of each calendar month. For the purposes of this
      calculation and the calculation required in Section 7.6 below, Debt and
      Consolidated liabilities of the Company shall not include the Subordinated
      Debt of the Company."

                                                                          Page 2
<PAGE>   3

      (f) The following event is hereby added to the end of Section 8.1 Events
of Default. of the Warehouse Agreement for all purposes:

            "(q) Centex fails to pay and perform its obligations pursuant to
      Section 6.15 of this Agreement by the deadline specified in that Section."

      (g) Article 9 of the Warehouse Agreement is hereby restated as follows:

            "9. Notices. Any notice, request or other communication required or
      permitted to be given under or in connection with this Agreement, the
      Notes or the other Loan Documents ("Notices") (except as may otherwise be
      expressly required therein) shall be in writing and shall be mailed by
      first class or express mail, postage prepaid, or sent by facsimile,
      confirmed by mailing (by first class or express mail, postage prepaid)
      written confirmation at substantially the same time as such facsimile, or
      personally delivered to an officer of the receiving party. All such
      communications shall be mailed, sent, delivered, or faxed to the parties
      hereto at their respective addresses or facsimile numbers as follows:

      If to the Company:            Mortgage Portfolio Services, Inc.
                                    5520 LBJ Freeway
                                    Suite 200
                                    Dallas, Texas 75240
                                    Attn:  James E. Hinton
                                    Facsimile:  (214) 821-7352
                                    Telephone:  (972) 341-8510

      With copies to Centex and Centex Corporation by facsimile (confirmed by
      mail) at their respective addresses specified below.

      If to the Guarantor:          NAB Asset Corporation
                                    4144 N. Central Expressway, Suite 900
                                    Dallas, Texas 75204
                                    Attn: Alan Ferree
                                    Facsimile:  (214) 821-3689
                                    Telephone:  (214) 860-1882

      If to Centex:                 Centex Financial Services, Inc.
                                    Attn:  Jim Hillsman
                                    2828 N. Harwood
                                    Dallas, Texas 75201-1516
                                    Facsimile: (214) 758-7814
                                    Telephone: (214) 981-7771

                                                                          Page 3
<PAGE>   4

      If to Centex Corporation:     Centex Corporation
                                    Attn:  Larry Angelilli
                                    2728 N. Harwood
                                    Dallas, Texas 75201-1516
                                    Facsimile: (214) 981-6858
                                    Telephone: (214) 981-6505

      If to Washington Mutual as Administrative Agent, Collateral Agent or a
      Lender:

                                    Washington Mutual Bank, FA
                                    Attn: Frank Hattemer
                                    3200 Southwest Freeway, Suite 2702
                                    Houston, Texas 77027
                                    Facsimile: (713) 543-6022
                                    Telephone:  (713) 543-6486

      If to Residential Funding Corporation:

                                    Residential Funding Corporation
                                    Attn:  Jim Clapp
                                    4800 Montgomery Lane, Suite 300
                                    Bethesda, Maryland 20814
                                    Facsimile: (301 215-6239
                                    Telephone: (301) 215-6288

      or at such other addresses or to such individual's or department's
      attention or at such other facsimile numbers as any party may have
      furnished the other party in writing. Any Notice addressed and mailed
      shall be deemed to be given when so mailed, except that Advance Requests,
      and communications related thereto shall not be effective until actually
      received by Administrative Agent or Company, as the case may be. Any
      Notice sent by facsimile shall be deemed to be given when receipt of such
      facsimile is acknowledged. Any Notice delivered in person shall be deemed
      to be given when receipted for by, or actually received by, an authorized
      officer of the receiving party."

      (h) EXHIBIT "T" to this Amendment is hereby added as EXHIBIT "T" to the
Warehouse Agreement for all purposes.

      Section 4. Representations and Other Agreements. (a) Company represents
and warrants that all of the representations and warranties contained in the
Warehouse Agreement and all instruments and documents executed pursuant thereto
or contemplated thereby are true and correct in all material respects on and as
of this date. Agent represents and warrants to Centex that it has provided to
Centex accurate and complete copies of the Warehouse Agreement and the Notes in
effect as of the date hereof.

      (b) Notwithstanding anything contained in the Warehouse Agreement, as
amended hereby, or in any other Loan Document to the contrary, Company agrees
that it shall not request or be entitled to receive any Advances on or after the
Termination Date.

                                                                          Page 4
<PAGE>   5

      (c) The maturity date of each Lender's Note is hereby renewed and extended
to sixty (60) days following the Termination Date.

      (d) The Loan Documents, as amended hereby, may not be amended or modified
by the Company, the Guarantor, the Agent, and the Lenders without the prior
written consent of Centex and Centex Corporation.

      (e) If at any time and from time to time Centex or Centex Corporation pays
to the Agent all Past Due Amounts specified in any Notice given by Agent in
accordance with Section 6.15 of the Warehouse Agreement, as amended hereby,
Company hereby directs the Agent to assign, release, and deliver, and Agent
hereby agrees to assign, release, and deliver, free and clear of the Agent's and
Lenders' Liens, to Centex, within two (2) Business Days of Agent's receipt of
Centex's or Centex Corporation's payment of all such Past Due Amounts in
immediately available funds, (i) all original Mortgage Notes (duly endorsed in
blank) held by Agent evidencing the Pledged Mortgages specifically relating to
such Past Due Amounts ("Past Due Mortgages"), and (ii) any and all other
Collateral Documents specifically relating to such Past Due Mortgages, if any,
held by the Agent under the Loan Documents. If the Agent thereafter receives any
Mortgage Notes or other Collateral Documents specifically relating to such Past
Due Mortgages (including Past Due Mortgages in respect of which Wet Advances
were made or sent to Investors for purchase) or any cash or non-cash proceeds
relating to any of the Past Due Mortgages, or any overpayments of amounts
payable by Centex under Section 6.15 of the Warehouse Agreement, Company hereby
directs Agent to assign, release, and deliver, and Agent hereby agrees to
assign, release and deliver, free and clear of Agent's and Lenders' Liens, to
Centex, promptly but in any event within two (2) Business Days of Agent's
receipt, all such Mortgage Notes, Collateral Documents, proceeds and
overpayments.

      Section 5. Severability. In the event any one or more provisions contained
in the Warehouse Agreement or this Amendment should be held to be invalid,
illegal or unenforceable in any respect, the validity, enforceability and
legality of the remaining provisions contained herein and therein shall not be
affected in any way or impaired thereby and shall be enforceable in accordance
with their respective terms.

      Section 6. Expenses. Company agrees to pay all out-of-pocket costs and
expenses (including reasonable attorney's fees and expenses) of the Agent and
the Lenders in connection with the preparation, operation, administration and
enforcement of this Amendment.

      Section 7. Ratification of Agreements. (a) Except as amended hereby,
Company ratifies and confirms that the Warehouse Agreement and all other Loan
Documents are and remain in full force and effect in accordance with their
respective terms and that all Collateral is unimpaired by this Amendment and
secures the payment and performance of all indebtedness and obligations of
Company under the Notes, the Warehouse Agreement, and all other Loan Documents,
as modified hereby.

      (b) Each of the undersigned officers of Company, Guarantor, Centex, and
Centex Corporation executing this Amendment represents and warrants that he has
full power and authority to execute and deliver this Amendment on behalf of the
party for whom he is executing this Amendment, that such execution and delivery
has been duly authorized by all necessary corporate action of such party, and
with respect to the Company and Guarantor, each of its respective officers
represents and warrants that the resolutions and affidavits previously delivered
to Agent, in connection

                                                                          Page 5
<PAGE>   6

with the execution and delivery of the Warehouse Agreement, are and remain in
full force and effect and have not been altered, amended or repealed in anywise.

      (c) Any reference to the Warehouse Agreement in any Loan Document shall be
deemed to be references to the Warehouse Agreement as amended hereby.

      (d) Except as amended hereby, each of the Agent and the Lenders ratifies
and confirms that the Warehouse Agreement and all other Loan Documents are and
remain in full force and effect in accordance with their respective terms.

      (e) Each of the undersigned officers of the Agent and the Lenders
represents and warrants that he has full power and authority to execute and
deliver this Amendment on behalf of the party for whom he is executing this
Amendment and that such execution and delivery has been duly authorized.

      Section 8. No Waiver. Company agrees that no Event of Default and no
Default has been waived or remedied by the execution of this Amendment by Agent
and Lenders, and any such Default or Event of Default heretofore arising and
currently continuing shall continue after the execution and delivery hereof.
Agent and Lenders represent and warrant to Centex that they are not aware of any
Default or Event of Default that is existing as of the date hereof.

      Section 9. Governing Law. This Amendment shall be governed by and
construed in accordance with the laws of the State of Texas and, to the extent
applicable, by federal law.

      Section 10. Counterparts and Gender. This Amendment may be executed in any
number of counterparts and all of such counterparts taken together shall be
deemed to constitute one and the same instrument. Each gender used herein shall
include and apply to all genders, including the neuter.

      Section 11. Joinder of Centex and Centex Corporation. (a) Centex is joined
herein to evidence its agreement to the terms, conditions and agreements
contained in this Amendment and to observe, pay and perform the obligations set
forth in Section 6.15 of the Warehouse Agreement, as amended hereby. Centex
hereby acknowledges that but for such agreements, Agent and Lenders would not
enter into this Amendment.

      (b) Centex Corporation hereby, unconditionally and absolutely, guarantees
to the Agent, on behalf of the Lenders, the prompt and punctual payment and
performance when due (whether at its maturity, by lapse of time, by
acceleration, or otherwise) of all indebtedness, liabilities, and obligations
("Guaranteed Obligations") of Centex under this Amendment and Section 6.15 of
the Warehouse Agreement, as amended hereby. The foregoing guaranty is an
absolute guaranty of payment and not a guaranty of collection. Centex
Corporation agrees to pay Agent the Guaranteed Obligations upon demand and all
of its out-of-pocket collection costs relating to the enforcement of Centex
Corporation's obligations hereunder, including any additional amount for
reasonable attorney's fees, if the Guaranteed Obligations are not paid by Centex
Corporation upon demand or if the obligations of Centex Corporation hereunder
are enforced by suit, or through probate or bankruptcy court or through any
judicial proceedings whatsoever. Centex Corporation hereby expressly waives each
and every right to which it may be entitled by virtue of the suretyship laws of
the State of Texas including, without limitation, any rights it may have
pursuant to Rule 31, Texas Rules of Civil Procedure, V.T.C.A. Civil Practice and
Remedies Code Section 17.00 and Chapter 34 of the Texas Business and Commerce
Code.

                                                                          Page 6
<PAGE>   7

Centex Corporation acknowledges that but for its guaranty the Agent and the
Lenders would not enter into this Amendment.

      Section 12. Further Assurances. Company agrees to do such further acts and
things and execute and deliver to Centex such additional assignments, powers and
instruments as are reasonably required by Centex to carry into effect the
release and delivery to Centex of the Mortgage Loans and other Collateral
required to be released and delivered to it under Section 4(e) hereof.

      SECTION 13. NO ORAL AGREEMENTS. THIS AMENDMENT AND THE OTHER LOAN
DOCUMENTS REPRESENT THE FINAL AGREEMENT BETWEEN THE PARTIES AND MAY NOT BE
CONTRADICTED BY EVIDENCE OF PRIOR, CONTEMPORANEOUS OR ORAL AGREEMENTS OF THE
PARTIES.

      THERE ARE NO UNWRITTEN ORAL AGREEMENTS BETWEEN THE PARTIES.

                            [Signature Pages Follow]

                                                                          Page 7
<PAGE>   8

      EXECUTED this 30th day of April, 2001.

                                        COMPANY:

                                        MORTGAGE PORTFOLIO SERVICES, INC.,
                                        a Delaware corporation

                                        By: s/s James E. Hinton
                                            ------------------------------------
                                        James E. Hinton, President

                                        NOTICE ADDRESS:

                                        Mortgage Portfolio Services, Inc.
                                        4144 North Central Expressway
                                        Suite 800
                                        Dallas, Texas 75204
                                        Attn:  James E. Hinton
                                        Facsimile: (214) 821-7352
                                        Telephone: (972) 341-8510

                                                                          Page 8
<PAGE>   9

                                        GUARANTOR:

                                        NAB ASSET CORPORATION,
                                        a Texas corporation

                                        By: s/s Alan Ferree
                                            ------------------------------------
                                        Name: Alan Ferree
                                        Title: SVP

                                        NOTICE ADDRESS:

                                        NAB Asset Corporation
                                        4144 N. Central Expressway, Suite 900
                                        Dallas, Texas 75204
                                        Attn: Alan Ferree
                                        Facsimile: (214) 821-3689
                                        Telephone: (214) 860-1882

                                                                          Page 9
<PAGE>   10

                               WASHINGTON MUTUAL BANK, F.A., successor by merger
                               to BANK UNITED, as Administrative Agent and a
                               Lender

                               By: s/s Patrick C. Freeman
                                   ---------------------------------------------
                                      Patrick C. Freeman, AVP
                                      Mortgage Banker Finance

                               NOTICE ADDRESS:

                               Washington Mutual Bank, F.A.,
                               successor by merger to Bank United
                               Attn: Frank Hattemer, Director
                               Mortgage Banker Finance
                               3200 Southwest Freeway, Suite 2702
                               Houston, Texas 77027
                               Facsimile: (713) 543-4292
                               Telephone: (713) 543-6486

                                                                         Page 10
<PAGE>   11

                                        RESIDENTIAL FUNDING CORPORATION,
                                        a Delaware corporation, as a  Lender

                                        By: s/s Jim Clapp
                                            ------------------------------------
                                        Name: Jim Clapp
                                        Title: Director

                                        NOTICE ADDRESS:
                                        Residential Funding Corporation
                                        Attn:  Thomas M. Clement
                                        4800 Montgomery Lane, Suite 300
                                        Bethesda, Maryland 20814
                                        Facsimile:  (301) 215-6288
                                        Telephone: (301) 215-6239

                                                                         Page 11
<PAGE>   12

                                        CENTEX FINANCIAL SERVICES,  INC.,
                                        a Nevada corporation

                                        By: s/s Larry Brown
                                            ------------------------------------
                                        Name: Larry Brown
                                        Title: Assistant Treasurer

                                        NOTICE ADDRESS:

                                        Attn:  Jim Hillsman
                                        2828 N. Harwood
                                        Dallas, Texas 75201-1516
                                        Facsimile: (214) 758-7814
                                        Telephone: (214) 981-7771

                                                                         Page 12
<PAGE>   13

                                        CENTEX CORPORATION,
                                        a Nevada corporation

                                        By: s/s Vicki A. Roberts
                                            ------------------------------------
                                        Name: Vicki A. Roberts
                                        Title: Vice President and Treasurer

                                        NOTICE ADDRESS:

                                        Attn:  Larry Angelilli
                                        2728 N. Harwood
                                        Dallas, Texas 75201-1516
                                        Facsimile: (214) 981-6858
                                        Telephone: (214) 981-6505

                                                                         Page 13

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