As far as Unreal/Unreal Tournament goes, a Voodoo 5 would be a good choice, as the unreal engine runs much better with Glide than it does with Direct3D.
If you're going to play anything else than UT, you probably want to get a GeForce2 GTS which can easily beat Voodoo5 in almost every aspect. If you have a lot of money you could get a GeForce2 Pro or Ultra. With these you'll be kicking some serious ass!
You should be aware that buying a new graphics card is a bad idea if your system is too slow to keep up. Then you could end up with the card waiting for data from the CPU all the time.
If you really want something out of a GeForce2, I'd suggest something in the vicinity of an Athlon 550 as an absolute minimum.
Whatever you do, don't get a Voodoo5. Nvidias GeForce2 series is so much better, both in terms of price and performance.