The 9100 PCI is probably the fastest one out there. It's an 8500 in disguise. If there's any way you can, replace your motherboard and get a Ti4200. It won't cost too much more ($130 altogether), but the system will be lots faster for gaming.
Overstock.com has ATI PCI 9100 64MB for $50.00 + $1.00 shipping...
<font color=red><b>The mind is in its own place, and in itself
Can make a Heav'n of Hell, a Hell of Heav'n.</b></font color=red>
John Milton, <i>Paradise Lost</i>, Book II