This is the system? http://support.gateway.com/s/PC/FX/F...X6800sp2.shtml

It mentions two types of GPU:

Graphics1
(Requires Discrete Graphics) ATI CrossFire™ dual card option
ATI Radeon™ HD 4850 graphics1, featuring:
512 MB video buffer memory
DirectX® 10
Shader Model 4.0

NVIDIA GTS 150 graphics, featuring:
1 GB video buffer memory
DirectX® 10
Shader Model 4.0
The latter is based on the earlier NV50/NV8x/9x (8000/9000) series GPUs which have been known to have problems with the first two TW games.