Trouble running video games on mbp 13" bootcamped

I have a macbook pro 13" and I've read that people with the same setup are playing Fallout 3 and other games pretty smoothly if not error free. At first (playing fallout 3) with medium display setting and 1200x800 resolution, the game runs fine with and almost perfect. But after 5 or so minutes of gameplay, it gets all choppy. Can anyone tell me what's going on here? Is my video card not up to it?

2.53GHz intel core 2 duo
4GB 1067MHz ddr3
nvidia 9400m

Fallout 3 is a bad port. It is full of bugs.

I'd say monitor your temps tho and see if you card is getting hot. Overheating cards can cause problems in games.

The first thing I'd recommend would be to upgrade your video drivers (you should be able to get them directly from NVIDIA). Also, what anti-virus software are you running?

how do i monitor the temperatures? is there a program?

i dont have any anti virus installed because i only bootcamped xp to play videogames. i dont go online on the xp side.
i did update the drivers. i thought that might be the problem, but it didnt help.