If you do not feel like waiting for the NVidia GeForce GTX 285 Mac Edition to finally arrive in mass, or would like to have it cheaper, you can use the extension set released by Netkas that will give you the ability to use a PC version of this card in a Mac Pro without requiring flashing its ROM.
Netkas even offer an universal extension able to work with most Pc version of Radeon and GeForce cards with Mac OS X Leopard:
http://rapidshare.de/files/47461448/Enabler_for_Nvidia_and_multiple_ATI_cards.pkg.html
Warning, this is a report only, as we did not validate it on our side. For the GeForce GTX 285 as well as the 260 and 275 models, you will need the specific drivers, not included yet in Mac OS X, you should be able to get them from the IRC channels (here).
We are amazed by the work released by those developers. It gives us the freedom to use any graphic card and to avoid being tight to Apple's decision to support the release of only very few graphic card models. However, you should not forget to carefully read the procedure as well as engage in such adventure if you are skilled enough to.
