Confederate, I Have a customer interested in the same thing you are doing, and I was wondering if you had to do anything special to get 3 video cards setup in your PC. Right now, I throw in a PCI card to match a dual head Matrox already installed and WinXP Pro comes up "device cannot start (code 10)" I have tried 3 different cards, all with that error.
:edit: Figured it out, I had to put the PCI adapter first in the BIOS and boot that. All is working )