I have a lot of crashes when doing away team missions. The gameplay is terrible in combat scenes. It happens a lot that the screen freezes for a sec.

And with big explosions the game tends to crash.

I have the following setup:
Intel I7 920
6GB Ram
HD5850 @ Catalyst 9.12
Windows 7 64 Bit.

My Brother does not have these problems:
AMD Phenom II 710
4GB Ram
HD4850 @ Catalyst 9.12
Windows 7 64 Bit.