Fra ocworkbench's FAQ:
Can I use AGP and PCIe cards together?
Yes. Since the AGP card needs the agp driver, you'll need to install the AGP first.
- Insert the AGP card ONLY, FOLLOW THE STEPS ABOVE
- Power down.
- Insert the PCIe card, and boot
- Install the PCIe card's driver
- reboot, go into BIOS
- Under "Advanced" menu >> goto "Chipset Configuration", and set "Primary Graphics Adaptor" to PCIe