My bet. You may need to set a BIOS setting to tell it which to use as the boot video. Look for AGP/PCI and set to AGP.
Beware this issue. I benchmarked an old Nvidia TNT2 against an onboard 3D card and the onboard won!
This card came with a dell desktop pc bought a couple of years ago. I would like to be able to move it to a new system amd 1200+ 512 ram 40 gb hd and onboard graphics. When i inserted it into the AGP slot and plugged the monitor in i just got a black screen. How do i fix this? Or is it not possible to use that card on this system?