Macworld is reporting that the current NVIDIA Quadro FX 4800 and GeForce GTX 285 drivers won't work with the upcoming Mac OS 10.5.8 update.  You'll need to update to the newest driver firmware before running the 10.5.8 update (which is apparently arriving soon!) or else you'll get a kernel panic upon restart.

Both cards are made for Mac Pro systems. The GeForce GTX 285 is offered by Nvidia manufacturing partner EVGA. It was released in June. The drivers are available for download from EVGA’s Web site. The latest Quadro FX 4800 drivers are available from Nvidia. The Quadro FX 4800 is a workstation-level graphics card offered as an optional add-on from the Apple Store.

For your troubles, you will apparently see as much as a 20% improvement in gaming performance.