Just installed new 3d card, computer running slow?

Ok here's my comp specs

Dell 2.8 Ghz, 512 Ram, Just installed a ATI Radeon X700

It seems like my computer is running really slow now, just using basic applications even. I think I deleted my old drivers using Driver Cleaner Pro, and I got the newest drivers for my new card I think.

When it comes to games the only game I can even get into is Gunz and I do notice the graphics look a lot better. But I"ve been trying to play Rome Total War, and Dungeon Seige II which used to run fine, but now Its taking like 10 minutes to load the opening screen, and the opening movies are soooo slow. They used to skip a tiny tiny bit with my old card, but now they run like in slow motion and take forever to load up. I was just wondering if anybody could tell me what the problem may be? If you need any more information just let me know. Thanks