I was very happy to find new 3dfx drivers online.  My old machine is a P3 600mhz, 256ram, which was (against my advice) upgraded to WinXP.  It has a Voodoo 5 5500 PCI, back when this was my primary machine (it is now my parents' computer) I was always shocked how well it did with newer games, especially Grand Theft Auto 3.

I installed the latest SFFT yesterday afternoon, I believe the machine had been using default VGA drivers from windows prior to that.  So far I've noticed quicker desktop performance, but it appears Windows is taking longer to load when the system is turned on - is this normal, or is it likely unrelated?

EDIT:

So here's the full specs-

Dell Dimension XPS T600 (1998 model)
Windows XP Pro SP2 (Came with Win98SE)
Intel Pentium III 600mhz
256mb SDRAM
Voodoo 5 5500 PCI (the system came with a Voodoo 3 3500 AGP, I upgraded later)