I have an agp x1950 pro 256mb, and it kicks butt. You can get them for around $200 if you shop around. It's argueably the fastest agp card you can get.
I'm assuming you are running an agp vid card slot.
Plus you can run folding@home on it, if you are so inclined. =)
Or if you can only spend just over $100, get it's younger sibling, the x1650, it's about 2/3 the speed of the x1950 from the benchmarks i've seen.
