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                                                                Exhibit 10.4

              AMENDMENT TO EMPLOYMENT AGREEMENT FOR EXECUTIVE OFFICER

     THIS AMENDMENT TO EMPLOYMENT AGREEMENT FOR EXECUTIVE OFFICER 
("Agreement") made the 13th day of December, 1998, between SYLVESTER, INC., a 
Texas corporation (the "Company"), and J. SHANE LONG ("Executive").

     WHEREAS, Executive and the Company have executed an Employment Agreement 
dated as of November 1, 1996 (the "Employment Agreement"); and

     WHEREAS, under an Agreement and Plan of Reorganization dated as of 
December 13, 1998 (the "Merger Agreement"), the Company will become a 
wholly-owned subsidiary of Tweety Inc., a California corporation ("Tweety"); 
as of the Effective Time (as defined in the Merger Agreement) (the "Merger"); 
and

     WHEREAS, at the Effective Time of the Merger, Tweety will assume the 
Employment Agreement and become the employer thereunder; and 

     WHEREAS, Executive and the Company desire to set forth in this Agreement 
the amended terms for Executive's continued employment following the Merger. 

     NOW, THEREFORE, in consideration of the mutual covenants and agreements 
herein contained, the parties agree as follows:

                                    FIRST

     The terms of this Agreement shall become effective only at the Effective 
Time of the Merger, at which time Tweety shall assume the Employment 
Agreement, as amended by this Agreement, and all references in such 
Employment Agreement and this Agreement to the "Company" shall be deemed to 
refer to Tweety. Paragraphs 1 and 2 of the Employment Agreement will be 
amended in their entirety to provide as follows:

"1.  EMPLOYMENT.  The Company hereby agrees to employ Executive and Executive 
hereby agrees to serve the Company on the terms and conditions set forth 
herein, for the period commencing on the Effective Time of the Merger and 
expiring on the date that is three (3) months following such date (unless 
sooner terminated as hereinafter set forth).  The term of this Agreement may 
be referred to herein as the "Period of Employment."

     2.   POSITION AND DUTIES.  Executive shall serve as the Senior Vice 
President of Worldwide Sales of the Company, performing the functions and 
duties as shall be prescribed from time to time provided that such functions 
and duties are consistent with and attendant to Executive's position or other 
positions that he may hold from time to time.  Executive shall devote his 
full working time and efforts to the business and affairs of the Company and 
the promotion of its interests and perform all duties and services on behalf 
of the Company necessary to carry out such functions."

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                                  SECOND

     Subparagraphs 3a, 3b and 3c of the Employment Agreement will be amended 
in their entirety to read as follows:

     "3.  COMPENSATION AND RELATED MATTERS.

          a.   BASE SALARY. Executive shall receive a base salary ("Base 
Salary") at the annualized rate of Two Hundred Fifteen Thousand Dollars and 
No/100 Cents ($215,000.00).  The term "Base Salary" as used in this Agreement 
shall mean, at any point in time, Executive's annual base salary at such 
time. The Base Salary shall be payable in substantially equal semi-monthly 
installments or in accordance with the Company's regular payroll practices.

          b.   INCENTIVE COMPENSATION.  In addition to Base Salary, Executive 
shall participate in the Company's incentive compensation plan for its senior 
executive management employees at a rate of 10% of his Base Salary and Sales 
Commissions. 

          c.   SALES COMMISSIONS.  In addition to Base Salary and Incentive 
Compensation, Executive shall be targeted to receive sales commissions equal 
to One Hundred Ten Thousand Dollars and No/100 Cents ($110,000.00) (as a 
multiplier or ratio of sales revenue) that shall be payable monthly on the 
fifteenth of the month following the month in which they are earned."  

                                  THIRD

     Paragraph 8(b) of the Employment Agreement will be amended in its 
entirety to provide as follows:

     "(b) If Executive is entitled to receive the Parachute Payment Amount 
under Paragraph 11, or if Executive remains employed with the Company through 
the Period of Employment and the Agreement terminates in accordance with 
Subparagraph 9(h) hereof, then the provisions of Subparagraph 8(a) shall not 
apply.

                                 FOURTH

     Subparagraph 9c of the Employment Agreement will be amended to delete 
therefrom Subsection (A) in its entirety.  Subsection (C) of the definition 
of "Good Reason" in Subparagraph 9d of the Employment Agreement will be 
amended in its entirety to reflect more clearly the original intent of the 
parties, to read as follows:

     "(C) without Executive's consent, a reduction of Executive's Base Salary 
to an amount less than previously determined and fixed for the immediately 
preceding twelve-month period by the Compensation Committee in accordance 
with Subparagraph 3(a) other than a reduction deemed necessary by the Board 
for all executive officers;"

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                                    FIFTH

     Paragraph 12 of the Employment Agreement will be amended in its entirety 
to provide as follows:

     "12. NOTICE.  For purposes of this Agreement, notices and all other 
communications provided for in the Agreement shall be in writing and shall be 
deemed to have been duly given when delivered or mailed by United States 
certified mail, return receipt requested, postage prepaid, addressed as 
follows:

     if to the Executive:

          At his home address as shown
          in the Company's personnel records;

     if to the Company:

          3Dfx Interactive, Inc.
          4435 Fortran Drive
          San Jose, CA  95134
          Attn: Secretary

or to such other address as either party may have furnished to the other in 
writing in accordance herewith, except that notices of change of address 
shall be effective only upon receipt."

     IN WITNESS WHEREOF, the parties have executed this Agreement on the date 
set forth above.

                                        STB SYSTEMS, INC.

/s/ J. Shane Long                       /s/ Willaim E. Ogle
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J. SHANE LONG                           By:
                                        Its.:  Chief Executive Officer
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