Have a dual dual-core G5 at work (4 cores total, I didn't repeat myself

) with a 6600 GT video card. The fellow using it has been complaining about performance of the card in Motion, and I have an XFX 8600 GTS card just sitting around at home. Is there anything I need to know to get it working, or any one know if it will even work?
Thanks heaps in advance.
EDIT: They're both PCI-Express, in case anyone asks.