I am planning on upgrading from an ATI Radeon 5450 to an ATI Radeon 6950. I need to know if my computer is compatible with it. It is an HPE-400F, with all the standard parts as far as I know. If i need to add anything to it, what, and what software will I need? If possible, tell me how to install a new card, I have never done this before. Please break it down for me as simple as possible.