Graphics Issue..Crashing

Ok when i get to the dollet tower, and im going up the elevator, its all fine, then it shows the sequence of biggs and wedge, then my characters come up and the cutscene begins....

If you dont kow what cutscene im talkin about, its the one when the generator kicks on and the wrench falls into teh turbines and stuff.....anyways......

When this happens, and when it gets to the point when the satellite shoots up and begins to open, it begins to lag, extremely bad.....and then it crashes....i have no idea why, any help you have would be greatly appreciated

Computer

1.5Ghz Intel Pentium M (Labtop)
512 MB Ram
Anything else you need to know jsut let me know :)