Try one of these.
http://www.google.com/search?hl=en&q=3dfx+Voodoo+3+graphics+driver
I just set up and old computer that runs windows 98. I can't figure out how to switch to 256bit color on the monitor.
System info:
AMD K6 2 500mhz
Soyo motherboard SY-5EMA+ V1.1
384mb sdram 3x128mb
3dfx Voodoo 3 graphics card (No set up disc)
Sound Blaster Audigy 2 soundcard (Can't find a driver either)
15gb Western Digital Hard drive
Samsung CD-ROM
Floopy drive
Any and all help would be great! MJ

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic