I think you’re stuck if you have a PowerMac G5 that uses the AGP graphic slot. Two of the best cards, ATI’s 9800 Pro and X800, are nearly impossible to find (Mac Sales lists both with a 27 day wait for shipment and that wait never seems to change). The 9600 Pro seems readily available, but it’s not nearly as good as the two cards above. You can always check eBay and see what’s there.