I have quite a similar configuration (apart from a GeForce and not a Geoforce <img src="/ubbthreads/images/graemlins/delight.gif" alt="" /> ) , and I didn't have any problems.
Well and I didn't have Direcx 9 at that time.
You could try to put more wave - buffers to the driver responsible for playing wave-sound-files.
If you have a sound-card, of course. (You didn't mention one.)
And you could try to reduce parameters in the GeForce driver, by the way, which version number has your GeForce driver ?
As a summary, I have the feeling as if this has something to do with sound, which is often very resource-hungry in terms of direct hardware access.
But I can't say since you haven't mentioned a soundcard yet ...
Last : Try to reduce the details from within the <img src="/ubbthreads/images/graemlins/div.gif" alt="" /> Menu ...
P.S.: Windows 98 had a Service Pack ? ... Didn't know that ...
