widescreen resolutions

I've seen people using lower widescreen resolutions to boost performance (1280x800, 1024x640, etc.) When I try to use these resolutions by plugging them into the .ini file, I crash on load up. Are the resolutions driver specific? I am using a 6800 GT with 84.25 drivers. Can't stand playing with the black bars on the side. I am about to just go buy the 360 version since I can't afford to upgrade my PC at the moment.

You have to add them to your custom resolutions on your desktop.

How do I do that? :o

Depends on which videocard you have.

ATI:
ATI Catalyst Control Center -> Display Manager

nVidia:
Desktop -> Properties -> Settings -> Video Card Tab -> Screen Res & Refresh Settings

thanks man.