Before I got my X800Pro I was using a 128mb 9600 (bog standard) with GW. I did initially have problems like you described but I downloaded the ATI removal tool from ATI's website. Having completely removed the ATI installation I swapped to using Omega Drivers. These are less of a system hog.
The 9600 will struggle a little in ports & around convoys but it is playable even with a little AA/AF.
The 9600's also had a issue with using the correct AGP bios setting. IIRC I turned mine down from 128 to 64, with no further problems.
FYI, I picked up my X800pro from e-bay for £80 (GB) and run with full AA/AF with no slowdowns at all.
How much system RAM do you have? Also, these crashes can be caused by on board sound hardware acceleration. Open your sound properties and turn it right down.
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