<PAGE>

                                                                   EXHIBIT 10.18

                                                                    CONFIDENTIAL

Confidential treatment has been requested with respect to portions of the
agreement indicated with an asterisk [*].  A complete copy of this agreement,
including the redacted items, has been separately filed with the Securities and
Exchange Commission.


                               AMENDMENT NO. 1 TO
                        SUBSCRIPTION SERVICES AGREEMENT

This Amendment No. 1 to Subscription Services Agreement ("Amendment") is entered
into as of September 15, 2000 and amends that certain Subscription and Services
Agreement ("Agreement") between Compaq Computer Corporation ("Client") and
pcOrder.com, Inc. ("pcOrder") dated June 16, 1999.

Now, therefore, the parties hereby agree as follows:

1. Sections 4.1 and 4.2.  Sections 4.1 and 4.2 of the Agreement are hereby
   --------------------
   amended and restated in their entirety to provide as follows:

 4.1  Client shall pay to pcOrder within forty five (45) days of each of the
      Effective Date and [*] thereof [*] as the Annual Subscription License Fee
      for the Software. Client shall pay to pcOrder within forty five (45) days
      of [*] of the Effective Date as the Annual Subscription Fee for the
      Software, (a) [*] if Client makes the Configuration Only Election pursuant
      to Section 14.7 on or before [*], or (b) [*] if Client does not make the
      Configuration Only Election on or before [*].

 4.2  If this Agreement is extended for a first Renewal Term pursuant to Section
      14.1, Client shall pay to pcOrder within forty five (45) days of the [*]
      of the Effective Date as the Annual Subscription License Fee for the
      Software, (a) [*] if Client makes the Configuration Only Election pursuant
      to Section 14.7 on or before [*], or (b) [*] if Client does not make the
      Configuration Only Election on or before [*]. If this Agreement is
      extended for a second Renewal Term pursuant to Section 14.1, Client shall
      pay to pcOrder within forty five (45) days of the [*] of the Effective
      Date as the Annual Subscription License Fee for the Software, (a) [*] if
      Client makes the Configuration Only Election pursuant to Section 14.7 on
      or before [*] or (b) [*] if Client does not make the Configuration Only
      Election on or before [*]. Thereafter, Client may extend this Agreement by
      paying to pcOrder within forty five (45) days of each subsequent
      anniversary of the Effective Date an amount that is equal to 100.0 % plus
      or minus the U.S. Consumer Price Index percentage for the previous
      calendar year times the prior year's Annual Subscription License Fee for
      the Software, but in any event the amount paid to pcOrder for such Renewal
      Term shall not be more than 110.0% of the prior year's Annual Subscription
      License Fee for the Software.

2. Section 14.2.7.  A new Section 14.2.7 is added to the Agreement that provides
   --------------
   in full as follows:

 14.2.7  By Client for convenience effective upon the [*] of the Effective Date,
         by providing written notice to pcOrder on or before [*] of its election
         to terminate the Agreement as of the [*]. It shall be a condition
         precedent to the effectiveness of such election that Customer pays to
         pcOrder on or prior to [*] all undisputed outstanding invoices that are
         received by Customer by [*].

3.  Section 14.7.  A new Section 14.7 is added to the Agreement that provides in
    ------------
    full as follows:

 14.7  Client shall have the right to terminate its license to all Software
       licensed under this Agreement, except the Configuration Software, by
       providing written notice of such election (the "Configuration Only
       Election") to pcOrder by the following dates: by [*] for the election to
       be effective as of the [*] of the Effective Date and for all periods
       following; by [*] for the election to be effective as of the [*] of the
       Effective Date and for all periods following, if any; or by [*] for the
       election to be effective as of the [*] of the Effective Date and for all
       periods following, if any. If Client makes the Configuration Only
       Election, the provisions of Section 14.5 of this Agreement shall apply to
       all Software, except the Configuration Software, effective as of the
       effective date of the election indicated in the previous sentence. For
       the purposes hereof, "Configuration Software" shall mean the
<PAGE>

                                                                    CONFIDENTIAL

       Server Software identified as pcOrder Backbone 3.2, CIM 2.0 (including
       the SBRave maintenance environment) and SalesBUILDER in Attachment E.

4. Payment of Year 2 Annual Subscription License Fee.  The parties acknowledge
   -------------------------------------------------
   that Client has deferred payment of the [*] Annual Subscription License Fee
   for Year 2 pending the negotiation of this Amendment. pcOrder agrees that
   that payment shall be considered to be timely paid under the Agreement if it
   is received by pcOrder by September 22, 2000.

5. Outstanding Invoices. Client hereby agrees that it will pay the undisputed
   --------------------
   outstanding invoices for consulting issued through July 31, 2000 totaling [*]
   by September 15, 2000 (other than invoice #COM032CON244 for [*]), net of a
   [*] credit asserted by Client (which is under investigation by pcOrder as of
   the date of this Amendment).


                  [REMAINDER OF PAGE INTENTIONALLY LEFT BLANK]

                                       2
<PAGE>

                                                                    CONFIDENTIAL

6.  May 1, 2000 Notice Letter.  Client hereby revokes and rescinds its notice
    -------------------------
    letter to pcOrder dated May 1, 2000 regarding the acceptance of the March
    deliverables of the eStation 3.2 product and hereby accepts delivery of all
    deliverables specified in the letter dated November 21, 1999 from pcOrder to
    Client. Notwithstanding the foregoing, pcOrder hereby agrees that it will
    use reasonable efforts, without charge to Client, to assist Client in the
    implementation of cookie-based session persistence (i.e., cookie stickies)
    with Cisco Local Director version 3.3 or higher to support sites that run
    Software.

7.  Schedule 1.  Schedule 1 to the Agreement is amended as set forth in the
    ----------
    attached Amendment No. 1 to Schedule 1.

8.  Schedule 2.  Schedule 2 to the Agreement is amended as set forth in the
    ----------
    attached Amendment No. 1 to Schedule 2.

9.  Schedule 3.  Schedule 3 to the Agreement is amended as set forth in the
    ----------
    attached Amendment No. 1 to Schedule 3.

10. Full Force and Effect.  The Agreement, as amended by this Amendment, remains
    ---------------------
    in full force and effect.

By signing below, each party acknowledges that it has read, understands, and
agrees to the terms of this Amendment:

pcOrder.com, Inc.:                     Compaq Computer Corporation:

/s/ Christina Jones                    /s/ R.V. Napier
-----------------------------------    ------------------------------------
By:  Signature                         By:  Signature

Christina Jones                        Robert V. Napier
-----------------------------------    ------------------------------------
Name                                   Name

President                              Sr. VP & Chief Information Officer
----------------------------------     ------------------------------------
Title                                  Title

                                       3
<PAGE>

                                                                    CONFIDENTIAL

                               AMENDMENT NO. 1 TO
                                   SCHEDULE 1

                   PROFESSIONAL CONSULTING SERVICES SCHEDULE

The Schedule 1 Professional Consulting Services Schedule ("Schedule") to the
Subscription Services Agreement between pcOrder.com, Inc. ("pcOrder") and Compaq
Computer Corporation ("Client") dated June 16, 1999 is hereby amended effective
September 15, 2000 as set forth in this Amendment No. 1 ("Amendment").

1.  Section 3.2.  A new Section 3.2 is added which provides in full as follows:
    -----------

    3.2  pcOrder shall make available the services of developers and modelers
         for the second and third years of the Agreement at the following hourly
         rates:

<TABLE>
<CAPTION>
Type of Service                       Description of Services                      Year 2             Year 3
----------------------------------------------------------------------------------------------------------------
<S>                       <C>                                                      <C>                <C>
Developer                 Classified as a "developer" by pcOrder or                [*]                [*]
                          Trilogy.  Primary role and responsibility
                          within organization is to develop products.
----------------------------------------------------------------------------------------------------------------
Senior Developer          Classified as a "developer" by pcOrder or                [*]                  [*]
                          Trilogy.  Primary role and responsibility
                          within organization is to develop products.
                          Has at least two years of development
                          experience with pcOrder or Trilogy products.
----------------------------------------------------------------------------------------------------------------
Senior CIM2 Modeler       Primary architect for design of CIM 2.0/CML and          See Schedule 2       [*]
                          responsible for implementation of CIM 2.0/CML.
----------------------------------------------------------------------------------------------------------------
CIM2 Modeler              Works under the direction of Sr. CIM 2 Modeler           See Schedule 2       [*]
                          in the implementation of CIM 2.0/CML.
----------------------------------------------------------------------------------------------------------------
SystemBuilder Modeler     Responsible for implementation of SystemBuilder          See Schedule 2       [*]
                          configuration rules in the SystemBuilder models.
----------------------------------------------------------------------------------------------------------------
</TABLE>

2. Full Force and Effect.  The Schedule, as amended by this Amendment, remains
   ---------------------
   in full force and effect.

By signing below, each party acknowledges that it has read, understands, and
agrees to the terms of this Amendment:

pcOrder.com, Inc.:                     Compaq Computer Corporation:

/s/ Christina Jones                    /s/ R.V. Napier
-----------------------------------    ------------------------------------
By:  Signature                         By:  Signature

Christina Jones                        Robert V. Napier
-----------------------------------    ------------------------------------
Name                                   Name

President                              Sr. VP & Chief Information Officer
----------------------------------     ------------------------------------
Title                                  Title

                                       4
<PAGE>

                                                                    CONFIDENTIAL


                               AMENDMENT NO. 1 TO
                                   SCHEDULE 2

                       DATA MAINTENANCE SERVICES SCHEDULE

The Schedule 2 Data Maintenance Services Schedule ("Schedule") to the
Subscription Services Agreement between pcOrder.com, Inc. ("pcOrder") and Compaq
Computer Corporation ("Client") dated June 16, 1999 is hereby amended effective
September 15, 2000 as set forth in this Amendment No. 1 ("Amendment").


1. Section 6.  Section 6 of the Schedule is hereby amended by deleting Sections
   ---------
   6.1 and 6.2 thereof and replacing it with the following:

   Client shall pay to pcOrder Annual Data Maintenance Fees according to the
   following schedule: (a) [*] on the Effective Date for the first twelve (12)
   months of Data Maintenance Services (which shall include Data Maintenance
   Services for High Volume, High End, and 3rd Party SKUs); and (b) for the
   second and third twelve (12) months of Data Maintenance Services, the fees in
   accordance with the following table:


<TABLE>
<CAPTION>
----------------------------------------------------------------------------------------------------------
        Service                Year 2 Rate              Year 3 Rate                Payment Schedule
----------------------------------------------------------------------------------------------------------
<S>                         <C>                    <C>                        <C>
Configuration Services      [*] for services       Time and materials by      Year 2 fees due on September
                                described in       mutually agreed AO.  See   22, 2000.  Year 3 fees
                                Section 8.1        Schedule 1 for rates.      payable in accordance with
                                                                              applicable AOs.
----------------------------------------------------------------------------------------------------------
Class/Categorization        See Section 8.3        See Section 8.3            Monthly in arrears.
 and Population
 Services (collectively
 "Data Compilation
 Services")
----------------------------------------------------------------------------------------------------------
</TABLE>

2.  Section 8.  A new Section 8 is added to the Schedule that provides in full
    ---------
    as follows:

   8.  SERVICE LEVELS

   8.1 The service levels set forth in Sections 2.1.2., 3.1.2. and 4.1.2. of
   this Schedule terminate effective June 16, 2000. For the period from July 16,
   2000 through July 16, 2001, pcOrder shall provide Client with up to [*] full-
   time dedicated personnel, each working up to 40 hours per week (with up to
   [*] such personnel working up to 50 hours per week), to provide configuration
   services, of which up to [*] personnel shall provide CIM 2.0 configuration
   services (including project administration) and up to [*] personnel shall
   provide SystemBuilder configuration services; provided, however that until
   October 30, 2000 pcOrder shall only be required to provide Client with at
   least [*] such full-time dedicated personnel. If Client authorizes in excess
   of [*] full-time personnel to perform CIM 2.0 configuration services or in
   excess of [*] full-time personnel to perform SystemBuilder configuration
   services, it shall pay for such services at the rate of [*] per month for
   each such additional person. Upon the request of Client for additional
   personnel, pcOrder shall use reasonable efforts to staff such request within
   45 days of such request. pcOrder shall give Client 30 days notice prior to
   removing any personnel providing configuration services to Client from the
   Client account, unless such notice is not possible because of the termination
   of such person's employment, illness or other reasons beyond pcOrder's
   control. In the event that personnel new to the Client account commence
   providing configuration services, pcOrder shall count each such personnel as
   one-half of a full-time employee for at least two weeks to account for ramp-
   up time.

                                       5
<PAGE>

                                                                    CONFIDENTIAL

   8.2  For any period after June 16, 2001, configuration services shall be
   performed on a time and materials basis by assignment order mutually agreed
   between the parties.

   8.3 On or after June 16, 2000, pcOrder shall provide Data Compilation
   Services for the Client Products and 3rd Party SKUs requested by Client, up
   to an aggregate of [*] per month, upon [*] business days of receipt of the
   request. Client shall pay for Data Compilation Services based on the number
   of Client Products and 3rd Party SKUs requested per month at a cost of [*]
   per Client Product or 3rd Party SKU requested, subject to a minimum aggregate
   cost of [*] per month. Each unique product identifier supplied by Client to
   pcOrder shall be counted as one unique Client Product or 3rd Party SKU, even
   if such identifier does not represent a valid product or if Client has
   already provided a different identifier for such product. For all purposes of
   this Section 8.3, a Bundled Product shall be counted as 3 Client Products. A
   "Bundled Product" means a customized product that consists of multiple
   manufacturer SKUs (including Client and/or third party) incorporated into a
   single product, including, but not limited to, CTO and BTO products. Client
   shall use reasonable efforts to identify products as Bundled Products when
   making a request to pcOrder. Either party may terminate the provisions of
   this Section 8.3 upon [*]; provided that Client's obligation to pay for all
   requests made prior to the date of termination shall survive. Notwithstanding
   the foregoing, the termination of this Section 8.3 shall not affect Client's
   right to continue using the content provided under this Schedule during the
   term of this Agreement.

3. Additional Content Services.  pcOrder hereby agrees that following the
   ---------------------------
   execution of this Amendment it shall negotiate with Client in good faith
   regarding the terms and pricing of providing additional content and/or
   content services to Client, including industry standard catalog, use of
   content separate from the Software, and use of content following termination
   of the Agreement.

4. Full Force and Effect.  The Schedule, as amended by this Amendment, remains
   ---------------------
   in full force and effect.

By signing below, each party acknowledges that it has read, understands, and
agrees to the terms of this Amendment:

pcOrder.com, Inc.:                     Compaq Computer Corporation:

/s/ Christina Jones                    /s/ R.V. Napier
-----------------------------------    ------------------------------------
By:  Signature                         By:  Signature

Christina Jones                        Robert V. Napier
-----------------------------------    ------------------------------------
Name                                   Name

President                              Sr. VP & Chief Information Officer
----------------------------------     ------------------------------------
Title                                  Title

                                       6
<PAGE>

                                                                    CONFIDENTIAL

                               AMENDMENT NO. 1 TO
                                   SCHEDULE 3

                     APPLICATION HOSTING SERVICES SCHEDULE

The Schedule 3 Application Hosting Services Schedule ("Schedule") to the
Subscription Services Agreement between pcOrder.com, Inc. ("pcOrder") and Compaq
Computer Corporation ("Client") dated June 16, 1999 is hereby amended effective
September 15, 2000 as set forth in this Amendment No. 1 ("Amendment").

1. Section 1.  Section 1 of Schedule 3 to the Agreement is hereby amended and
   ---------
   restated in its entirety to provide as follows:

   For the first twelve months following June 16, 1999, the fee for the
   Application Hosting Services performed by pcOrder is [*] per year for the
   first [*] servers supporting Client at the Hosting Site and an additional fee
   of [*] per server per year for each server in addition thereto. For the
   twelve month period from June 16, 2000 to June 16, 2001, the fee for the
   Application Hosting Services performed by pcOrder is [*] per server per month
   for each server in a High Availability Environment. For the twelve month
   period from June 16, 2001 to June 16, 2002, the fee for the Application
   Hosting Services performed by pcOrder is [*] per server per month for each
   server in a High Availability Environment. For the purposes hereof, "High
   Availability Environment" shall mean a hosting facility that has raised
   floor, redundant power, controlled temperature and air quality, and sensitive
   fire suppression systems. In addition, the PESO production farm shall be
   deemed to be hosted in a "High Availability Environment" for the purposes of
   this Section regardless of where it is actually hosted. For all periods after
   June 16, 2000, pcOrder shall bill Client for Application Hosting Services
   monthly in arrears. The addition of servers to the High Availability
   Environment shall require the written authorization of the Vice President of
   e-Commerce Development of Client and of the Vice President, Internet Services
   of pcOrder.

2. Full Force and Effect.  The Schedule, as amended by this Amendment, remains
   ---------------------
   in full force and effect.

By signing below, each party acknowledges that it has read, understands, and
agrees to the terms of this Amendment:

pcOrder.com, Inc.:                     Compaq Computer Corporation:

/s/ Christina Jones                    /s/ R.V. Napier
-----------------------------------    ------------------------------------
By:  Signature                         By:  Signature

Christina Jones                        Robert V. Napier
-----------------------------------    ------------------------------------
Name                                   Name

President                              Sr. VP & Chief Information Officer
----------------------------------     ------------------------------------
Title                                  Title

                                       7