I ran my demo on my Athlon Thunderbird (probably first breed), 800 Mhz, over 300 MB RAM, GeForce 2 GTS (Elsa Gladiac 32) Win98SE and a the newest NVidia driver, and of course Directx 90b.
No problems.
By the way, I had turned everything off in my NVidia driver settings. Maybe you can try this ?