I've tried using an ATI AGP card with a voodoo 3 in a PCI slot (g5 pmac here) with no luck. It senses the voodoo 3, but when I launch a game (wipeout2097 for example) and select the voodoo 3 as the output, it "tries" to push an image to the other monitor via the voodoo but then freezes. This goes for any number of things I tried pushing to the other screen.