I have a Dell 530S (slimline) with Windows XP Professional. My son wants to play his Call of Duty, World at War game; It says the video card doesn't support it. The Dell tech told me the small video card is in the motherboard but a new more powerful one can be added. He said to make sure it's the low one to fit in there. What is the best video card to use to play these games and is it difficult to add?