I want to play games like (Thief, Thief 2 metal age) etc on my current computer system which had Nvidia Geforce Ultra 8800 graphics card, etc.

The problem is that the game freezes . Tell me how to make it compatible with this system?

OS Vista Ultimate 64-bit
Motherboard (MSI) P6N Diamond
VGA (MSI) Pair Geforce 8800 Ultra SLI
Sound (Creative) Xi-Fi Fatal1ty
RAM (Corsair) Dominator 4GB
HDD (Hitachi) Ultrastar A7K1000 a pair of 1000GB connected in RAID 0
PSU (Enermax) Galaxy 1000watts