First, updating to sp2 might help.
Second, you have a very low amount of RAM, for XSI. With XSI, you can say that you're in safe zone when you have 512, but ideally it would be more than 1 gig.
Other possible sources might something in your scene.... have you noticed any specific conditions when the crash occur?
Hope this helps
Salutations - Cheers
Bernard Lebel