Well.. I had Quake3 and Unreal Tournament running on XFree86 v4.0.1 withouth too much trouble.
If you already have XFree86 v4 running, then you just might just need to install the NVIDIA drivers. I just recently had loads of problems with mine after updating to NVIDIAs latest drivers. Turns out that was only because I didn't explicitly follow the instructions that are on NVidia's website. Follow those instructions and you should do fine.
BTW.. last night.. I got Counter-Strike working via WINE.