By fit, do you mean physically fit in a spacial sense, or do you mean fit the slot(s) that you have? And DX9/10/11 really doesn't mean much, that's just the dx version it can run. Just because a card has dx10 doesn't mean it can run games flawlessly, it still needs some other goods specs. A price range and power supply would also be nice to know.
edit: dkamm pretty much got all those specs :D