remove PCIE card, install PCI card, boot into PC BIOS, set primary display adapter to PCI
shut down, install PCIE card (along with PCI card), reboot, you now have display via PCI card
flash your PCIE cards BIOS, remove PCI card, boot into windows, voila.
i say voila - but its easier to write it than do it
EDIT i just saw its another PCIE card, well if you have 2 PCIE lanes for fitting 2 cards, you can still do it (just remember to flash the correct card, atiflash -i gives you adapter numbers)