I assume you have done the basics such as upgrade your video driver. My first thought is that is the issue since Win7 is so new. A couple of other items you want to do also:
#1, make sure your NOT on high fidelity on your graphic settings. This causes game crashes and the infamous black screen during game play on some cards.
#2, your load time at the beginning was long. You can attribute load loads to virtual memory swaps if once the game starts it runs fine. You need to reduce your graphic settings so it is not loading so many textures (medium will work if you have 4 gigs on your graphics card and 4 on your motherboard).
Items #1 & 2 may or may not fix the problem, but they will improve your game play so worth trying it out.
Did some research on your Graphics card. It might have DDR2 or DDR3 memory chips instead of GDDR. It also has a slow clock compared to desktop cards. You should run in DirectX 9 mode and not 10. Also, your screen resolution should be at maximum 1024x768. Graphic setting for textures should be put on LOW instead of medium as mentioned in #2 above for your card (you have 1 GB graphics memory).