I have the same setup you have, except 3 gb RAM; I'm running GTA IV on mine with low settings; it's borderline playable, pretty low frame rate.
Even with the low framerate though, it's pretty fun game, well worth installing. I'll let you know if I find any good tweaks.
Rob
Macbook unibody 2.4 / 3 gb / 9400M
.Net Framework 3.5
DOX Optimised NVidia drivers 180.84 (Balanced; Performance mode was unusable)
XP 32 bit SP3
In 800x600 with everything turned down to bare minimum (Low/Low/1/1), benchmarks at 17.46 fps 85% CPU 52% Mem 59% Video Mem
Again, playable, but barely. Worth it though!