Thanks to all who have replied; some useful info.
FunkyMunky, you mentioned "full size 16x PCI express slots". How do I know if mine are 16x? I have already tried a cheap standard PCI card and it gave my PC a severe stomach upset. It stopped booting up and I had to remove the card and ended up having to reload windows due to various corrupted files. I assumed that was because PCI is not compatable with PCI express. (It was a Club Radeon 9250 card)