On the now obsolete PowerPC PCIe macs I would not have gone for a Quadro FX - it's not massively faster than the 7800 and occupies 2 slots. However, with the new Mac Pros they've sorted out the 2 slot graphics card problem by offsetting the other PCIe slots one slot, so you can have a massive graphics card without loosing valuable PCIe slots.

However, nVidia have traditionally only sold their grpahics cards with Macs and NOT retail.

Best wishes,

Hugh
Altered State Ltd