<PAGE>   1
                                                                   EXHIBIT 10.8

                        AMENDMENT TO CREDIT AGREEMENT


         THIS AMENDMENT TO CREDIT AGREEMENT ("Amendment"), dated as of March
29, 2001, is entered into by and among CERIDIAN CORPORATION, a Delaware
corporation, (the "Borrower"), each lender from time to time party hereto
(collectively, the "Lenders" and individually, a "Lender"), BANK OF AMERICA,
N.A., as the Administrative Agent and L/C Issuer (the "Administrative Agent"),
and FLEET NATIONAL BANK, as the Syndication Agent.

                                   RECITALS

         A.       The Borrower, Lenders, and Administrative Agent are parties
to a Credit Agreement dated as of January 31, 2001 (the "Credit Agreement")
pursuant to which the Administrative Agent and the Lenders have extended
certain credit facilities to the Borrower.

         B.       The Borrower has requested that the Lenders agree to certain
amendments of the Credit Agreement and the schedules thereto.

         C.       The Lenders are willing to amend the Credit Agreement and
the schedules thereto, subject to the terms and conditions of this Amendment.

         NOW, THEREFORE, for valuable consideration, the receipt and adequacy
of which are hereby acknowledged, the parties hereto hereby agree as follows:

         1.       Defined Terms.  Unless otherwise defined herein, capitalized
terms used herein shall have the meanings, if any, assigned to them in the
Credit Agreement.

         2.       Amendments to Credit Agreement.

                  (a)      Section 7.07(a)(i) of the Credit Agreement shall be
amended by deleting such subsection in its entirety and replacing it with the
following:

                           (i)      declare and make (A) the Distribution, or
                  (B) dividend payments or other distributions payable solely
                  in shares of its common stock (and solely in respect of
                  fractional shares, cash of a de minimis amount), or (C)
                  pursuant to the terms of a shareholder rights agreement
                  approved by Borrower's board of directors, distributions on
                  a ratable basis to all then-existing common stock
                  shareholders payable solely in shares of preferred stock of
                  the Borrower, or rights or options to acquire additional
                  shares of its common stock upon the occurrence of certain
                  events, and provided there exists no Default or Event of
                  Default, cash payments by the Borrower upon the redemption
                  or purchase by the Borrower of such rights or options, not
                  exceeding in the aggregate for all such payments from and
                  after the Closing Date $200,000;

                  (b)      Schedule 5.21 of the Credit Agreement shall be
amended by deleting it in its entirety and replacing it with Schedule 5.21 as
attached hereto;

                                      1.

<PAGE>   2

                  (c)      Section 6.15(a) of the Credit Agreement shall be
amended by deleting the clause beginning with "provided, however," and
continuing to the end of the subsection and replacing it with the following:

                  provided, however, that (i) that if any additional
                  Subsidiary so incorporated, created or acquired is a Foreign
                  Subsidiary of a Subsidiary incorporated within the United
                  States, in no event shall more than 65% of the capital stock
                  of any such Foreign Subsidiary be required to be so pledged,
                  and (ii) no such pledge of capital stock shall be required
                  if such Foreign Subsidiary is a Subsidiary of another
                  Foreign Subsidiary.

         3.       Representations and Warranties.  The Borrower hereby
represents and warrants to the Administrative Agent and the Lenders as
follows:

                  (a)      No Default or Event of Default has occurred and is
continuing.

                  (b)      The execution, delivery and performance by the
Borrower of this Amendment have been duly authorized by all necessary
corporate and other action and do not and will not require any registration
with, consent or approval of, notice to or action by, any Person (including
any Governmental Authority) in order to be effective and enforceable. The
Credit Agreement as amended by this Amendment constitutes the legal, valid and
binding obligations of the Borrower, enforceable against it in accordance with
its respective terms, without defense, counterclaim or offset.

                  (c)      All representations and warranties of the Borrower
contained in the Credit Agreement are true and correct.

                  (d)      The Borrower is entering into this Amendment on the
basis of its own investigation and for its own reasons, without reliance upon
the Administrative Agent and the Lenders or any other Person.

         4.       Effective Date.  This Amendment will become effective on the
date shown first above (the "Effective Date"), provided that each of the
following conditions precedent is satisfied:

                  (a)      The Administrative Agent has received from the
Borrower and each of the Required Lenders a duly executed original (or, if
elected by the Administrative Agent, an executed facsimile copy) of this
Amendment, together with a duly executed Guarantor Acknowledgment and Consent
in the form attached hereto (the "Consent").

                  (b)      The Administrative Agent has received from the
Borrower and all guarantors a copy of a resolution passed by the board of
directors of such corporation, certified by the Secretary or an Assistant
Secretary of such corporation as being in full force and effect on the date
hereof, authorizing the execution, delivery and performance of this Amendment
(or the Consent, as applicable).

                  (c)      All representations and warranties contained herein
are true and correct as of the Effective Date.

                                      2.

<PAGE>   3

         5.       Miscellaneous.

                  (a)      Except as herein expressly amended, all terms,
covenants and provisions of the Credit Agreement are and shall remain in full
force and effect and all references therein to such Credit Agreement shall
henceforth refer to the Credit Agreement as amended by this Amendment. This
Amendment shall be deemed incorporated into, and a part of, the Credit
Agreement.

                  (b)      This Amendment shall be binding upon and inure to the
benefit of the parties hereto and thereto and their respective successors and
assigns. No third party beneficiaries are intended in connection with this
Amendment.

                  (c)      This Amendment shall be governed by and construed in
accordance with the law of the State of New York.

                  (d)      This Amendment may be executed in any number of
counterparts, each of which shall be deemed an original, but all such
counterparts together shall constitute but one and the same instrument. Each of
the parties hereto understands and agrees that this document (and any other
document required herein) may be delivered by any party thereto either in the
form of an executed original or an executed original sent by facsimile
transmission to be followed promptly by mailing of a hard copy original, and
that receipt by the Administrative Agent of a facsimile transmitted document
purportedly bearing the signature of a Lender or the Borrower shall bind such
Lender or the Borrower, respectively, with the same force and effect as the
delivery of a hard copy original. Any failure by the Administrative Agent to
receive the hard copy executed original of such document shall not diminish the
binding effect of receipt of the facsimile transmitted executed original of such
document of the party whose hard copy page was not received by the
Administrative Agent.

                  (e)      This Amendment, together with the Credit Agreement,
contains the entire and exclusive agreement of the parties hereto with reference
to the matters discussed herein and therein. This Amendment supersedes all prior
drafts and communications with respect thereto. This Amendment may not be
amended except in accordance with the provisions of Section 10.01 of the Credit
Agreement.

                  (f)      If any term or provision of this Amendment shall be
deemed prohibited by or invalid under any applicable law, such provision shall
be invalidated without affecting the remaining provisions of this Amendment or
the Credit Agreement, respectively.

                  (g)      The Borrower covenants to pay to or reimburse the
Administrative Agent, upon demand, for all costs and expenses (including
allocated costs of in-house counsel) incurred in connection with the
development, preparation, negotiation, execution and delivery of this Amendment.

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

                                      3.

<PAGE>   4




                                      CERIDIAN CORPORATION


                                      By: /s/ JOHN H. GRIERSON
                                         --------------------------------------

                                      Title: Vice President and Treasurer
                                            -----------------------------------


                                      BANK OF AMERICA , N.A., as
                                      Administrative Agent, a Lender and L/C
                                      Issuer


                                      By: /s/ CHITT SWAMIDASAN
                                         --------------------------------------

                                      Title: Principal
                                            -----------------------------------


                                      FLEET NATIONAL BANK,  as a Lender

                                      By: /s/ RICK ANDERSON
                                         --------------------------------------

                                      Title: Group Manager
                                            -----------------------------------

                                      U.S. NATIONAL ASSOCIATION, as a Lender


                                      By: /s/ ELLIOT J. JAFFEE
                                         --------------------------------------

                                      Title: Senior Vice President
                                            -----------------------------------

                                      THE CHASE MANHATTAN BANK, as a Lender


                                      By: /s/ CAROL A. KORNBLUTH
                                         --------------------------------------

                                      Title: Vice President
                                            -----------------------------------

                                      4.

<PAGE>   5



                                      THE BANK OF NEW YORK, as a Lender

                                      By: /s/ KRISTEN E. TALABER
                                         --------------------------------------

                                      Title: Vice President
                                            -----------------------------------


                                      BNP PARIBAS, as a Lender


                                      By:
                                         --------------------------------------

                                      Title:
                                            -----------------------------------

                                      BEAR STEARNS CORPORATE LENDING INC., as
                                      a Lender

                                      By:
                                         --------------------------------------

                                      Title:
                                            -----------------------------------

                                      CITIZENS BANK OF MASSACHUSETTS, as a
                                      Lender


                                      By: /s/ ERRIN SIAGEL
                                         --------------------------------------

                                      Title: V.P.
                                            -----------------------------------

                                      THE ROYAL BANK OF SCOTLAND PLC, as a
                                      Lender


                                      By: /s/ LEE MORSE
                                         --------------------------------------

                                      Title: Vice President
                                            -----------------------------------


                                      5.


<PAGE>   6








                     GUARANTOR ACKNOWLEDGMENT AND CONSENT



         The undersigned, each a Guarantor with respect to Borrower's
Obligations to Administrative Agent and the Lenders under the terms of the
Credit Agreement, each hereby (i) acknowledge and consent to the execution,
delivery and performance by Borrower of the foregoing Amendment to Credit
Agreement dated as of March ___, 2001 (the "Amendment"), and (ii) reaffirm and
agree that the respective Guaranty as to which each of the undersigned is
party, and all other Loan Documents and agreements executed and delivered by
the undersigned to Administrative Agent and the Lenders in connection with the
Credit Agreement, are in full force and effect without defense, offset or
counterclaim.

         All capitalized terms used herein and not otherwise defined shall
have the meanings assigned to them in the Credit Agreement.

         This Guarantor Acknowledgment and Consent may be executed in any
number of counterparts, each of which shall be deemed an original, but all
such counterparts together shall constitute but one instrument.



                                   NEW CERIDIAN CORPORATION

                                   By: /s/ JOHN H. GRIERSON
                                      -------------------------------------

                                   Title: Vice President and Treasurer
                                          ---------------------------------

                                   ARBITRON HOLDINGS INC.

                                   By: /s/ JOHN H. GRIERSON
                                      -------------------------------------

                                   Title: Vice President and Treasurer
                                          ---------------------------------


                                      6.

<PAGE>   7


                                                                  SCHEDULE 5.21

                         CAPITALIZATION; SUBSIDIARIES


                   Information as of the Effectiveness Date

         1.       Borrower's capitalization as of the Effectiveness Date:

                  No. shares authorized: 500,000,000

                  No. shares issued: 161,685,596

                  No. shares outstanding: 145,681,462

                  Please note that the shares listed above are subject to a
reverse stock split at a ratio of one-for-five. The reverse stock split will
be effective immediately after the Spin-Off Consummation Date.



         2.       Following is a list of Borrower's Subsidiaries as of the
                  Effectiveness Date:


<TABLE>
<CAPTION>
-----------------------------------------------------------------------------------------------------------------------
                                                                                                       NO. OF SHARES
                                                     STATE OR OTHER          PERCENTAGE OF VOTING       AUTHORIZED/
                                                    JURISDICTION OF          SECURITIES OWNED BY         ISSUED &
SUBSIDIARY                                            ORGANIZATION             IMMEDIATE PARENT         OUTSTANDING
-----------------------------------------------------------------------------------------------------------------------
<S>                                            <C>                         <C>                       <C>
Arbitron Holdings Inc. (First Tier Arbitron
subsidiary) formed in October 2000             Delaware                    100%                      1,000/1,000
-----------------------------------------------------------------------------------------------------------------------
CSW Research Ltd. (First Tier subsidiary of                                                          410,000/
Arbitron Holdings, Inc.)                       United Kingdom              100%                      405,000
-----------------------------------------------------------------------------------------------------------------------
Euro-Fieldwork Ltd. (Second Tier Arbitron
subsidiary, First Tier subsidiary of CSW
Research Ltd.)                                 United Kingdom              100%                      1,000/1,000
-----------------------------------------------------------------------------------------------------------------------
Ceridian Infotech (India) Private Limited                                                            8,400,000/
(First Tier Arbitron subsidiary)               India                       100%                      1,712,374
-----------------------------------------------------------------------------------------------------------------------
ABR Information Services, Inc.                 Florida                     100%                      N/A
-----------------------------------------------------------------------------------------------------------------------
     ABR Employer Services, Inc.               Florida                     100%                      N/A
-----------------------------------------------------------------------------------------------------------------------
     ABR Properties, Inc.                      Florida                     100%                      N/A
-----------------------------------------------------------------------------------------------------------------------
     BMC Consultants, Inc.                     Colorado                    100%                      N/A
-----------------------------------------------------------------------------------------------------------------------
</TABLE>

                                      7.

<PAGE>   8

<TABLE>
<CAPTION>
-----------------------------------------------------------------------------------------------------------------------
                                                                                                       NO. OF SHARES
                                                     STATE OR OTHER          PERCENTAGE OF VOTING       AUTHORIZED/
                                                    JURISDICTION OF          SECURITIES OWNED BY         ISSUED &
SUBSIDIARY                                            ORGANIZATION             IMMEDIATE PARENT         OUTSTANDING
-----------------------------------------------------------------------------------------------------------------------
<S>                                            <C>                         <C>                       <C>
     Ceridian Benefits Services, Inc.
     (f/k/a ABR Benefits Services, Inc.)       Florida                     100%                      N/A
-----------------------------------------------------------------------------------------------------------------------
     Ceridian Retirement Plan Services, Inc.
     (f/k/a ABR Retirement Plan Services,
     Inc.)                                     Florida                     100%                      N/A
-----------------------------------------------------------------------------------------------------------------------
     Charing Company, Inc.                     Wisconsin                   100%                      N/A
-----------------------------------------------------------------------------------------------------------------------
     Chowning, Ltd.                            Wisconsin                   100%                      N/A
-----------------------------------------------------------------------------------------------------------------------
         The Barrington Group                  Wisconsin                   100%                      N/A
-----------------------------------------------------------------------------------------------------------------------
     Matthews, Malone & Associates, Ltd.       Arizona                     100%                      N/A
-----------------------------------------------------------------------------------------------------------------------
     MidAtlantic 401(k) Services, Inc.         Virginia                    100%                      N/A
-----------------------------------------------------------------------------------------------------------------------
     Western Pension Service Corporation       California                  100%                      N/A
-----------------------------------------------------------------------------------------------------------------------
         Ceridian Investors Advisors, Inc.
         (f/k/a ABR Investment Advisors,
         Inc.)                                 Florida                     100%                      N/A
-----------------------------------------------------------------------------------------------------------------------
Arbat Middle East E.C. (held in trust)
(inactive)                                     Bahrain                     100%                      N/A
-----------------------------------------------------------------------------------------------------------------------
Ceridian Canada Holdings, Inc.                 Delaware                    100%                      N/A
-----------------------------------------------------------------------------------------------------------------------
     Ceridian Canada Ltd.                      Canada                      100%                      N/A
-----------------------------------------------------------------------------------------------------------------------
         33444651 Canada Ltd.                  Canada                      100%                      N/A
-----------------------------------------------------------------------------------------------------------------------
     Ceridian Performance Partners Ltd.        Canada                      100%                      N/A
-----------------------------------------------------------------------------------------------------------------------
Ceridian Holdings U.K. Limited                 United Kingdom              100%                      N/A
-----------------------------------------------------------------------------------------------------------------------
     Centrefile Limited                        United Kingdom              100%                      N/A
-----------------------------------------------------------------------------------------------------------------------
         Centrefile APS Limited                United Kingdom              100%                      N/A
-----------------------------------------------------------------------------------------------------------------------
         Centrefile (Mauritius) Ltd.           Mauritius                   100%                      N/A
-----------------------------------------------------------------------------------------------------------------------
     Ceridian Performance Partners Limited     United Kingdom              100%                      N/A
-----------------------------------------------------------------------------------------------------------------------
         Usertech UK Limited                   United Kingdom              100%                      N/A
-----------------------------------------------------------------------------------------------------------------------
</TABLE>

                                      8.

<PAGE>   9

<TABLE>
<CAPTION>
-----------------------------------------------------------------------------------------------------------------------
                                                                                                       NO. OF SHARES
                                                     STATE OR OTHER          PERCENTAGE OF VOTING       AUTHORIZED/
                                                    JURISDICTION OF          SECURITIES OWNED BY         ISSUED &
SUBSIDIARY                                            ORGANIZATION             IMMEDIATE PARENT         OUTSTANDING
-----------------------------------------------------------------------------------------------------------------------
<S>                                            <C>                         <C>                       <C>
Ceridian Tax Services, Inc.                    California                  100%                      N/A
-----------------------------------------------------------------------------------------------------------------------
Comdata Network, Inc.                          Maryland                    100%                      N/A
-----------------------------------------------------------------------------------------------------------------------
     Comdata Network Inc. of California        California                  100%                      N/A
-----------------------------------------------------------------------------------------------------------------------
     Comdata Telecommunications Services,
     Inc.                                      Delaware                    100%                      N/A
-----------------------------------------------------------------------------------------------------------------------
     International Automated Energy Systems,
     Inc.                                      Florida                     100%                      N/A
-----------------------------------------------------------------------------------------------------------------------
     Permicom Permits Services, Inc.           Canada                      100%                      N/A
-----------------------------------------------------------------------------------------------------------------------
     Stored Value Systems, Inc.                Delaware                    100%                      N/A
-----------------------------------------------------------------------------------------------------------------------
Computing Devices International Satellite
Services, Inc.                                 Delaware                    100%                      N/A
-----------------------------------------------------------------------------------------------------------------------
Partnership Group, Inc., The                   Pennsylvania                100%                      N/A
-----------------------------------------------------------------------------------------------------------------------
Plan Ware Inc. (inactive)                      Pennsylvania                100%                      N/A
-----------------------------------------------------------------------------------------------------------------------
POWERPAY.COM INC.
(f/k/a Ceridian Small Business Solutions,
Inc.)                                          New Jersey                  100%                      N/A
-----------------------------------------------------------------------------------------------------------------------
User Technology Services, Inc.                 New York                    100%                      N/A
-----------------------------------------------------------------------------------------------------------------------
</TABLE>


3.       Following is a list of Borrower's Arbitron Subsidiaries as of the
Effectiveness Date:

<TABLE>
<CAPTION>
-----------------------------------------------------------------------------------------------------------------------
SUBSIDIARY                                                          STATE OR OTHER JURISDICTION OF ORGANIZATION
-----------------------------------------------------------------------------------------------------------------------
<S>                                                          <C>
Arbitron Holdings Inc.                                       Delaware
-----------------------------------------------------------------------------------------------------------------------
     CSW Research Limited                                    United Kingdom
-----------------------------------------------------------------------------------------------------------------------
         Euro-Fieldwork Limited                              United Kingdom
-----------------------------------------------------------------------------------------------------------------------
Ceridian Infotech (India) Private Limited                    India
-----------------------------------------------------------------------------------------------------------------------
</TABLE>

                                      9.

<PAGE>   10

4.       Following is a list of Borrower's Material Subsidiaries as of the
Effectiveness Date:

<TABLE>
<CAPTION>
----------------------------------------------------------------------------------------------------------------------
MATERIAL SUBSIDIARIES                                        STATE OR OTHER JURISDICTION OF ORGANIZATION
----------------------------------------------------------------------------------------------------------------------
<S>                                                          <C>
ABR Information Services, Inc.                               Florida
----------------------------------------------------------------------------------------------------------------------
Comdata Network, Inc.                                        Maryland
----------------------------------------------------------------------------------------------------------------------
</TABLE>


               Information as of the Spin-Off Consummation Date

1.       Following is a list of Borrower's Arbitron Subsidiaries after the
Spin-Off Consummation Date:

<TABLE>
<CAPTION>
----------------------------------------------------------------------------------------------------------------------
                                                                                                     NO. OF SHARES
                                                                           PERCENTAGE OF VOTING       AUTHORIZED/
                                       STATE OR OTHER JURISDICTION OF      SECURITIES OWNED BY          ISSUED &
SUBSIDIARY                                       ORGANIZATION                IMMEDIATE PARENT         OUTSTANDING
----------------------------------------------------------------------------------------------------------------------
<S>                                    <C>                               <C>                       <C>
Arbitron Holdings Inc.                 Delaware                          100%                      1,000/1,000
----------------------------------------------------------------------------------------------------------------------
                                                                                                   410,000/
     CSW Research Limited              United Kingdom                    100%                      405,000
----------------------------------------------------------------------------------------------------------------------
         Euro-Fieldwork Limited        United Kingdom                    100%                      1,000/1,000
----------------------------------------------------------------------------------------------------------------------
                                                                                                   8,400,000/
Ceridian Infotech (India) Private
Limited                                India                             100%                      1,712,374
----------------------------------------------------------------------------------------------------------------------
</TABLE>


2.       There will not be any Material Subsidiaries of the Borrower as of the
Spin-Off Consummation Date.


                                     10.