Download CPU-Z so you can find out what motherboard you have, then Google that motherboard. Anyway with an old thing like that if you have PCI-E, which I doubt, then a 3650, 9500GT or a 4650 would be the way to go. Anything faster would be bottlenecked by the system. Heck the 4650 would be pretty bottlenecked by that system. If you have AGP then it's best if you go with a 3650 or 2600. Whatevers cheaper. Anyway you may have to upgrade your RAM as well, since you only have 512, if you actually want to play any games.