You should look on the actual motherboard to see if it has a pcie or agp graphics slot, if it's pcie, pretty much any modern card will be compatible, though as said, it will be bottlenecked by your cpu/motherboard
Bottlenecking is when either your CPU or GPU is too slow so one component has to wait for the other. It's like walking with your Grandparent , and you have to wait for him / her .
You'll need new ram and a new motherboard to go with that new cpu as well, along with a decent power supply to run it all...basically you're starting from ground zero to move past Pentium 4 era stuff...