Can't get my Radeon 4650 card to work, help!

I just recently bought a Radeon 4650 grahpics card for my dell 530s (slim) to upgrade from using the integrated card and i keep getting the black screen. When I switch back to the integrated card it works fine. It says I need to disable the integrated drivers, which I have and I'm running windows xp, but doing so isn't allowing the card to work. My power supply is 250 and so I've heard others have been able to run their graphics card with no problem. Has any one ran into any problems or can help me on how to solve this, I would greatly appreciate it.