|Before you even consider a gaming video card, you have to check your power supply specs. If you don't have enough wattage & amperage on the +12v rail, it will HAVE to be upgraded. And don't forget that you have a old P4 single core CPU & an AGP slot. Your system is outdated & really isn't worth throwing a lot of money at. Even the crappy Atom CPU that's used in netbooks is faster than your P4:|
But if you insist:
GeForce 7950GT AGP - al least $125 (new)
500W PSU - at least $50 for something decent
1GB DDR400 - at least $40
You'd be invest over $200 in a system that's probably not worth $100.