I have a DP 2.3 G5 (the one with the radeon 9600 128MB), and I just got the X800 for my G5, and I want to swap the 9600 to my old MDD DP 1ghz G4, can I do that?
This information is on the Accelerate your Mac site:
Q: Can I use a OEM Mac 9600 Pro card in anything but a G5 tower?
A: Like the BTO 9800 and Nvidia FX 5200 cards, As-is, the 9600 Pro card will only work in a G5 tower currently.
However, Eric Murphy sent a link to his article on Mac 9600 Pro card mods to run in 4x AGP G4 towers that shows mods needed for the 8x AGP card to run in an older 4x AGP slot system. (He used a MDD G4.) Later pages include benchmarks in UT2003 and Halo.
Note: The card will not work even with the mod in a 2x AGP slot Mac (i.e. Sawtooth, GigaBit Ethernet, etc.) due to the voltage difference