There is some deep magic going on with the modifications made to the kexts buried inside of the 9f23 installer.

I could never figure out what it was, but it allowed my 7900GTX to work with no problems. (er ah, also bios patched it to enable all 512MB of ram)

I'm having the same problem now on a 8800GTS. Going to see if this old technique will work...

Funny part about the 7900... I gave that card away to a relative who wanted to use it for SLi on his windows rig. It didn't work due to the bios patch. :-O

Thankfully I had a backup of the original rom so he was able to reverse it. :-D