Looks like it can take any of these:
NVIDIA GeForce 7950 GTX 512MB Video Module
NVIDIA GeForce Quadro FX 256 Video Module
NVIDIA GeForce Go 7900 series Video Module
NVIDIA GeForce Go 7800 256MB Video Module
NVIDIA GeForce Go 6800 ULTRA 256 Video Module
NVIDIA GeForce Go 6800 256 Video Module
This may be similar to your laptop:
http://www.flickr.com/photos/jay_dugger/sets/72157604986917052I can't find a specific guide for tearing that Nb down - the video is normally under the keyboard though.