I'm interested in what GeForce 6 card was used here?
i dont know what drivers people use to make it available to OS9 (or if that is even neccessary) but every example i saw until now were geforce 6x and 7x taken from the apple G5 models.
It just takes the video setting from Open Firmware, you can set the screen to a compatible resolution/bit depth in OS X and it will save that somehow to Open Firmware and the Mac OS ROM will just use that for OS 9.
Sadly 'NDRV's work a lot different with GeForce cards and everything pasted the GF4 lack a classic Mac OS Rom based 'NDRV'.
That's why I went to the trouble to test this with an ATI card as the OS X 'NDRV's are normally compatible with the classic Mac OS, and it was with the X800/FireGL X3 ROM. While we don't get any GFX acceleration at least we can change the screen resolution and bit depth in OS 9.
I also tested with my QS 800Mhz and it works just fine with the Apple 30" display in both OS 9 and OS X, so we can at least say the QS 800Mhz doesn't suffer from the AGP race condition that some QS and DA's suffer from. I have a few 733Mhz QS's and a 867mhz model sold as Education without the L3 cache that the production model had, I'll test those when I get time.
The Radeon 9600 Mac/PC edition also supports Dual-Link DVI on one port, but also suffers from the AGP Race Condition bug in some DA/QS models, but good luck finding one, they are rare as hen's teeth.