I was gonna suggest grabbing the newest drivers, but I'm betting you've already done that. Are there any S3 "enthusiast user" messageboards like Rage3D where people hack together slightly newer/updated driver files?
My stupid ATI Rage Pro Mobility chip in my Compaq Armada M300 lappy sucks a fat one and will always continue to do so... However after about 13 different trials with hacked pieces, I was able to get a single driver put together that does somewhat-ok DX8 3d (enough to play UnrealTournament at 512x384x16), mediocre OGL (enough to play Quake I at 512x384x16) and still is able to work correctly in DOS with extended ANSI characters (don't ask, heh)
Basically they just give you a list of components (DLL files, VXD files, etc) and you group them together for what kinds of performance you want. And then install them from a ubiquiteous INF file you can download...