All I know is that my dad (who works an IT job for credibility) told me the card would need to fit the BTX standard, though most cards don't seem to be built for it. I'm not sure if any of the standards are interchangeable. The computer itself is a Dell Optiplex 580 Desktop (the middle option, not the Mini-Tower or Small Form Factor.)
I'd prefer an NVIDIA, but at this point, I don't care. I've done too much searching to have those sorts of expectations

If you can help me out, it would be greatly appreciated.