I used 3 graphic cards in my Dell E510 which is 2 years before model with P4 630. I used X1300, 8500GT and the HD3870 both are work fine. What you need to do is see the display info at starting moment and Press the function key as the screen show and go inside the BIOS to save the new change of video card, I know the Dell BIOS is fool but they need you to do so. Whenever I added more memory or change display card, it required me to do so in order to boot into Windows. You boot the Windows in Safety mode and uninstall the ATI catalyst and reboot your windows.