VULCAN VENTURES INC, SC 13D, EX-99.3, 2000-08-15

VULCAN VENTURES INC
SC 13D, EX-99.3, 2000-08-15

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<PAGE>   1


EXHIBIT 99.3


JOINT FILING AGREEMENT

     We, the signatories of the statement to which this Joint Filing Agreement
is attached, hereby agree that such statement is filed, and any amendments
thereto filed by either or both of us will be filed, on behalf of each of us.

     Dated August 11, 2000.
           ----------------

                               VULCAN VENTURES INCORPORATED

                               By: /s/ WILLIAM D. SAVOY
                                   -------------------------------------------
                                   William D. Savoy, Vice President

                               /s/ PAUL G. ALLEN
                               -------------------------------------------
                               Paul G. Allen