<PAGE>

[LETTERHEAD]

December 18, 1997

Austin Commercial, Inc.
3535 Travis Street, Suite 300
Dallas, Texas 75204-1466

                                       
                        LIMITED NOTICE TO PROCEED NO.1
           WATERVIEW TECHNOLOGY CENTER PHASE I - RICHARDSON, TEXAS

Gentlemen:

This "Limited Notice to Proceed," having an effective date of December 18, 
1997, is your authorization to proceed with the Scope of Work defined in 
Attachment "A". The Guaranteed Maximum Cost to Owner for Contractor's 
performance of this Limited Notice to Proceed Work is not to exceed 
$3,777,420, including Contractor's Fee of $127,735. Applicable Conditions of 
this Limited Notice to Proceed are listed in Attachment "A".

                                   OWNER:

                                   STB SYSTEMS, INC.

                                   BY /s/ Bryan F. Keyes
                                     -----------------------------------
                                        Bryan F. Keyes
                                        Vice President


                                   ACCEPTED BY CONTRACTOR:

                                   AUSTIN COMMERCIAL, INC.


                                   BY /s/ Steve Warnick
                                     -----------------------------------
                                        Steve Warnick
                                        Vice President

                                   DATE:     December 18, 1997

<PAGE>
                                       
                                 ATTACHMENT 'A'
                                       TO
                        LIMITED NOTICE TO PROCEED NO. 1
                       WATERVIEW TECHNOLOGY CENTER PHASE I
                               RICHARDSON, TEXAS


I.   SCOPE OF WORK TO BE PERFORMED BY CONTRACTOR UNDER THIS LIMITED NOTICE TO
     PROCEED

     A.   Layout Work, Civil and Site Work including Clearing, Grading and Fill,
          Utilities, Paving, etc. - all in accordance with the following
          documents:

            PROJECT MANUAL (Specifications) Titled - SITEWORK CONSTRUCTION
            PACKAGE - Dated November 25,1997 - Consisting of Divisions and
            Sections listed in the Table of Contents

            DRAWINGS - Titled - SITEWORK PACKAGE FOR CONSTRUCTION - Consisting
            of the following Sheets having latest date indicated:

                      Sheet No. and Title                 Latest Date
                      -------------------                 -----------
                ----  Cover Sheet & Index of Drawings       11/26/97   (1)
                C-1   Cover Sheet & Index of Drawings       11/25/97
                C-4   Grading/Erosion Control Plan          11/25/97
                C-5   Erosion Control Details               11/25/97
                C-6   Drainage Area Map                     11/25/97
                C-7   Storm Sewer Plan                      11/25/97
                C-8   Storm Sewer Profiles                  11/25/97
                C-9   Paving/Dimension Control Plan         11/25/97
                C-10  Paving Details                        11/25/97
                C-11  Water & Sewer Plan                    11/25/97
                C-12  Water & Sewer Profiles                11/25/97
                C-13  Prevention Plan Narrative             11/25/97
                C-14  Prevention Plan Narrative             11/25/97
                C-15  Storm Water Pollution Prevention Plan (Not Dated) (2)

                    CITY OF RICHARDSON STANDARD CONSTRUCTION DETAILS

                C-1   Water                                 05/08/97
                C-2   Water                                 04/19/96
                C-3   Sanitary Sewer                        04/19/96
                C-4   Storm Sewer                           04/19/96
                C-5   Street                                05/--/97
                C-8   Misc. Details                         04/19/96
                C-9   Screening Wall Brick/Sidewalk         04/19/96  (3)


            (1) Disregard issue date of drawings listed on this sheet.
            (2) Manual Pages on this sheet have latest date of Feb. 1993.
            (3) Issued for Standard Sidewalk Details Only.

            General Notes:
                (A)  Reinforced concrete paving to be 3000 psi - 5" or 6" thick
                     (as scheduled) on 6" compacted fill with P.I. between 8
                     and 20.  Refer to alternate description on Drawing Sheet
                     C9.

                                      A-1
<PAGE>

ATTACHMENT 'A' TO LIMITED NOTICE TO PROCEED NO. 1
WATERVIEW TECHNOLOGY CENTER PHASE I - RICHARDSON, TEXAS

                (B)  Water lines shown on Drawing Sheet C11 are included in the
                     scope of this Limited Notice to Proceed.  Installation of
                     the 12" water lines and a portion of the 8" water line are
                     "On Hold" pending further study by the City.  Refer to
                     attached drawing SK-C11 dated 12/15/97 for location of
                     water lines "On Hold."
                (C)  Sanitary sewer lines shown on Drawing Sheet C11 are
                     included in the scope of this Limited Notice to Proceed. 
                     Installation of sanitary sewer lines are "On Hold" pending
                     further study by the City.  Refer to attached drawing 
                     SK-C11 dated 12/15/97 for location of sanitary sewer lines
                     "On Hold."

     B.   Foundation Work and Level One Structural Slab Work including Crawl
          Space Grading and Drainage and Under Floor Mechanical/Electrical Work
          - all in accordance with the following documents.

            PROJECT MANUAL (Specifications) Titled - STRUCTURAL FOUNDATIONS AND
            FIRST FLOOR PACKAGE - Dated November 17,1997 - Consisting of
            Divisions and Sections listed in the Table of Contents.

            DRAWINGS - Titled - FOUNDATION AND FIRST FLOOR PACKAGE FOR
            CONSTRUCTION - Consisting of the following Sheets having latest
            date indicated:

                       Sheet No. and Title                     Latest Date
                       -------------------                     -----------
                ----   Cover Sheet & Index of Drawings           11/21/97  (1)
                S1.01  General Notes                             11/21/97
                S2.01  Foundation Plan                           11/21/97
                S2.02  Level 1 Framing Plan                      11/21/97
                S3.01  Foundation Details                        11/21/97
                S4.01  Concrete Details                          11/21/97
                S5.01  Column Schedule                           11/21/97
                S6.01  Misc. Schedules                           11/21/97
                S6.02  Misc. Schedules                           11/21/97
                ME1.03 Under Floor Plan-Mechanical/Electrical    11/21/97
                C1     Crawl Space Grading and Drainage          11/21/97

                       For Information Only
                       --------------------
                S2.03  Level 2 Framing Plan                      11/21/97
                S2.04  Level 3&4 Framing Plan                    11/21/97
                S2.05  Roof Framing Plan                         11/21/97
                A1.01  Project Standards                         11/21/97
                A2     Level 1 Floor Plan                        11/21/97
                A3     Level 2 Floor Plan                        11/21/97
                A4     Typical Floor Plan                        11/21/97
                A6     Roof Plan                                 11/21/97
                A9     Building Elevations                       11/21/97
                A11    Building Sections                         11/21/97
                DD-1   Typical Floor Plan - Mechanical           11/03/97
                DD-2   Roof Plan - Mechanical/Electrical         11/03/97
                DD-3   Mechanical Details                        11/03/97
                DD-4   Electrical Riser                          11/03/97

            (1) Disregard drawings listed on this sheet.

                                      A-2
<PAGE>

ATTACHMENT 'A' TO LIMITED NOTICE TO PROCEED NO. 1
WATERVIEW TECHNOLOGY CENTER PHASE I - RICHARDSON, TEXAS

            General Note
                (A)  A "Jack Hole" for the future hydraulic elevator near
                     column line C-4 is included in the scope of this Limited
                     Notice to Proceed.

     C.   Light Pole Bases and Underground Conduit for Site Lighting and
          Electrical Work - all in accordance with the following drawing:

                         Sheet No. and Title           Latest Date
                         -------------------           -----------
                ME1.1    Site Plan Electrical            12/02/97

     D.   Contractors General Conditions Work for the Project, including
          necessary Mobilization, Permits, Insurance, Drawing Reproduction,
          Materials Testing and Construction of Exterior Mock-up Panel. NOTE:
          This Limited Notice to Proceed incorporates all work authorized in
          attached December 1, 1997 letter.

     E.   Preparation of Miscellaneous Shop Drawings and Prepurchases not
          required for this Limited Notice to Proceed Work but which may be
          required prior to contracting for the Work. The Maximum Cost to Owner
          for this Authorization is limited to $55,000. The sum of which is
          included in the Guaranteed Maximum Cost of this Limited Notice to
          Proceed.

          NOTE: ATTACHED IS A BREAKDOWN OF THE GUARANTEED MAXIMUM COST
          APPLICABLE TO THIS LIMITED NOTICE TO PROCEED. THE FOLLOWING ALLOWANCES
          ARE INCLUDED.

          Printing and Reproduction Charges                 $        30,000 (1)
          Permits & Fees                                    $        10,000 (2)
          Utility Charges                                   $        30,000 (3)
          Materials Testing                                 $        60,000
          Misc. Shop Drawing Preparation and Prepurchases   $        55,000 (4)

          (1)   Allowance subject to increase for printing and reproduction
                charges in excess of $35,000.
          (2)   For permits and fees (if any) that have not been waived by the
                City. Development Fees waived by the City consist of: Platting
                Fee, Site Plan Fee, Plan - Review Fee and Landscape Plan Review
                Fee.
                Building/Engineering Inspections Fees waived by the City
                consist of: Engineering Inspection Fees, Building Permit Fees.
          (3)   For temporary and check out power charges.
          (4)   For preparation of misc. shop drawings and prepurchases not
                required for this Limited Notice to Proceed work but which may
                be required prior to contracting for the Work.


II.  CONDITIONS OF THIS LIMITED NOTICE TO PROCEED

     A.   Upon receipt of this "Limited Notice to Proceed", Contractor shall
          proceed with the Work and shall continue with the performance of the
          Work upon receipt of either subsequent Limited Notices to Proceed or
          an Unlimited Notice to Proceed.

          Contractor agrees to achieve substantial completion of the Work
          consisting of the construction of a four story shell office building
          containing a gross floor area of approximately 210,000 SF and all
          related site improvements not later than 300 calendar days after date
          of this Limited Notice to Proceed.

                                      A-3
<PAGE>

ATTACHMENT 'A' TO LIMITED NOTICE TO PROCEED NO. 1
WATERVIEW TECHNOLOGY CENTER PHASE I - RICHARDSON, TEXAS

          Additionally, Contractor agrees to substantially complete the Work as
          necessary to allow the Interior Finish Out Work (other than Shell
          Building Finishes) to commence by Contractor or by Owner's other
          contractor(s) not later than 190 calendar days after date of this
          Limited Notice to Proceed. Contractor is in agreement that if
          Contractor is authorized in a timely manner to perform this Interior
          Finish Out Work (in excess of Shell Building Finishes) that
          substantial completion of both the Shell Office Building Work and the
          Interior Finish Out Work (in excess of Shell Building Finishes) can be
          achieved simultaneously.

          Contractor shall notify Owner in a timely manner if and when
          subsequent Limited Notices to Proceed are required in order to
          maintain Contractor's Schedule.

     B.   During the performance of this or subsequent Limited Notice to Proceed
          Work, Owner and Contractor expect to execute a Construction Contract
          for all Work in connection with the construction of the Phase I Shell
          Office Building and Site Improvements. The form of Contract shall be
          substantially similar to the Construction Contract Dated November 19,
          1997. Applicable terms and conditions of referenced Construction
          Contract apply to this "Limited Notice to Proceed."

     C.   Certificates evidencing the insurance coverage required of Contractor
          by the attachment titled CONTRACTOR'S INSURANCE REQUIREMENTS are to be
          submitted to Owner before commencing work. Additionally, Contractor
          shall take out an All Risk Builder's Risk Insurance policy insuring
          the interest of Owner, Contractor, Subcontractor and 
          Sub-subcontractors and which shall include but not be limited to, the
          perils of Fire, Lightning, Wind storm, Hurricane, Hail, Explosion,
          Riot, Civil Commotion, Smoke, Aircraft, Land Vehicles, Vandalism and
          Malicious Mischief, etc., in an amount equal to 100% of the contract
          sum (but not including non-insurable items). Contractor shall provide
          Certificates of such insurance to Owner.

     D.   Contractor is not required by this "Limited Notice to Proceed" to
          provide a performance bond or labor and material payment bond. 
          However, prior to execution of the Construction Contract, Owner may
          require Contractor to provide such bonds.

     E.   Prior to execution of the Construction Contract for the Phase I Shell
          Office Building and Site Improvements, Owner and Contractor shall
          mutually agree upon a Guaranteed Maximum Price for the Work which is
          currently estimated at $13,760,000, including budget allowance of
          $350,000 for Landscape Improvements/Graphics and $160,000 for
          extension of city water and sanitary sewer utilities serving the
          building, the cost of which is to be reimbursed to Owner by the City.

          The following is not included in above estimated amount.

                Contractors Payment Performance Bonds

                Interior Finish Out Work (in excess of Shell Building Finishes)

                                      A-4
<PAGE>





                     A Schematic of the Construction Site.





<PAGE>

                      BREAKDOWN OF GUARANTEED MAXIMUM COST
                  APPLICABLE TO LIMITED NOTICE TO PROCEED NO. 1

            WATERVIEW TECHNOLOGY CENTER PHASE I - RICHARDSON, TEXAS

<TABLE>
<S>                                                                         <C>
A.   Layout Work, Civil and Site Work including Clearing, Grading, Fill,
     Utilities, Paving, etc.                                                $1,394,625
     (Amount includes $160,000 for extension of City water and sanitary
     sewer utilities serving the building, the cost of which is to be
     reimbursed to Owner by the City).


B.   Foundation Work and Level One Structural Slab Work including Crawl
     Space Grading and Drainage and Under Floor Mechanical/Electrical Work.  1,396,150


C.   Lightpole Bases and Underground Conduit for Site Lighting and
     Electrical Work.                                                           25,000


D.   Contractors General Conditions Work for the Project, including
     Necessary Mobilization, Permits, Insurance, Drawing Reproduction,
     Materials Testing and Construction of Exterior Mock-up Panel.             778,910


E.   Preparation of Misc. Shop Drawings and Prepurchases not required for
     this Limited Notice to Proceed Work but which may be required prior
     to Contracting.                                                            55,000
                                                                            ----------
                                                                            $3,649,685


     Contractor's Fee                                                          127,735
                                                                            ----------

     Guaranteed Maximum Cost - LIMITED NOTICE TO PROCEED NO. 1              $3,777,420
</TABLE>

<PAGE>

[LETTERHEAD]

December 1, 1997


Mr. Bruce Lane
Austin Commercial, Inc.
3335 Travis Street, Suite 300
Dallas, Texas 75204-1466

RE: WATERVIEW TECHNOLOGY CENTER PHASE 1 - RICHARDSON, TEXAS

Dear Mr. Lane:

This letter shall serve as your authorization to:
     -    Move trailers and other temporary structures onto the site and set up
          your office compound and staging area where shown on attached site
          plan.  Install construction fence as necessary.
     -    Construct Exterior Mock-up Panel in accordance with attached HKS
          Memorandum dates November 25, 1997, and drawing A-1.  Mock-up Panel to
          be located where shown on attached site plan.
     -    Perform general layout and field engineering work.
     -    In preparation for the December 4th Ground Breaking Ceremony, mow
          grass and place gravel fill material within area shown on attached
          site plan.

It is understood that you will secure permits related to this authorized work 
and will submit Certificates evidencing the insurance coverage typically 
provided by Austin Commercial, Inc to STB Systems, Inc., prior to moving onto 
the site.

During the week of December 8, 1997, STB anticipates authorizing Austin by 
Limited Notice to Proceed No. One to commence Site and Building Foundation 
Work. It is understood that prior to the issuance of Limited Notice to 
Proceed No. One the amount STB is obligated to pay Austin related to this 
authorization work shall not exceed $75,000.00.

Sincerely,
STB Systems, Inc.


/s/ Bryan F. Keyes
Bryan F. Keyes                               Accepted December 2, 1997
Treasurer                                    AUSTIN COMMERCIAL, INC.


                                                  /s/ Bruce Lane
cc:  Garth Hodge - The Amend Group           By:  Bruce Lane
     Ray Wood - The Amend Group                   Project Manager

<PAGE>

                                 Contractor's
                            Insurance Requirements

The contractor shall purchase from and maintain in a company or companies 
lawfully authorized to do business in the state of Texas and with an A.M. 
Best's rating acceptable to the owner, the following insurance, in the 
following amounts, which shall, with the exception of the worker's 
compensation policy, be endorsed in all policies to include STB Systems, Inc. 
as additional insured. All policies shall be endorsed to include a waiver of 
subrogation in favor of STB Systems, Inc. its directors, officers and 
employees. Policy shall provide that STB Systems, Inc. shall be given thirty 
days prior written notice of any alteration or termination of coverage.

Contractor shall be responsible to verify that subcontractors are in 
compliance with the insurance provisions of this Agreement. Owner reserves 
the right to reject any subcontractor who cannot demonstrate proof of the 
insurance coverage required hereunder.

1.   COMMERCIAL GENERAL LIABILITY

     Policy is to be written on a standard ISO occurrence version of the 
Commercial General Liability form, or its equivalent, which includes coverage 
for premises operations, products-completed operations, independent 
contractors liability, personal injury liability, contractual liability, and 
explosion, collapse and underground coverage.

     Limits:

     $1,000,000 per occurrence bodily injury and property damage
     $1,000,000 personal and advertising injury
     $2,000,000 general aggregate (to apply on a per project basis)
     $2,000,000 products/completed operations limit
     $10,000 Medical Expense (any one person)

     COMPLETED OPERATIONS COVERAGE WILL BE MAINTAINED FOR AT LEAST 5 YEARS AFTER
     PROJECT COMPLETION.

2.   BUSINESS AUTOMOBILE COVERAGE

     Policy shall cover all owned, non-owned and hired vehicles used in 
connection with the work.

     Limits:

     $1,000,000 per occurrence combined single limit for bodily injury and
     property damage.

<PAGE>

3.   WORKERS COMPENSATION

     Coverage placed as required by Texas State Law and including Employer's
     Liability Insurance with a limit of not less than $500,000 per occurrence.


4.   EXCESS LIABILITY COVERAGE

     Coverage placed shall be at least as broad as primary Commercial General
     Liability, Business Automobile Liability and Employer's Liability policies
     with an occurrence limit of liability of no less than $10,000,000.

Certificates of Insurance shall be sent to STB Systems, Inc prior to 
commencement of the Work and shall provide for thirty (30) calendar days 
prior written notice of cancellation be given to STB Systems, Inc. 
Certificate should note that applicable policies have been endorsed to name 
STB Systems, Inc. as an additional insured and that policies have been 
endorsed with waivers of subrogation in favor of STB Systems, Inc.