It's an ATI Mobility Radeon X1600.

I don't know, how do I find that out?

How do I update it?

I've installed all the expansion packs up to seasons. My game crashes when I try to save it and either quit or go into the neighbourhood and then my computer restarts itself. I think the specifications for my pc should be fine, it's an XP. Could anyone tell me what's wrong with it and how to fix it?  Thanks.