|PCI-e > AGP > PCI|
If your board only has standard PCI slots, you're screwed. If you have an AGP slot & your current card is a 7600GS, I see no point in upgrading. If you never upgraded the power supply, you'd most likely have to do that to be able to run a better video card. And considering the cost of a decent PSU + a decent AGP gaming card, you'd have to spend well over $100. IMO, you'd just be throwing your money away on an outdated system.