What are some things to keep in mind for upgrading a graphics card? Interface type? Power supply? It's a ATI Radeon HD 4600 Series in a prebuilt computer. Really old. 5 years, and it's not holding up all that amazingly to the games I'm playing right now. I don't want to go out and buy a new one only to find I can't use it for some reason that I should have known beforehand.