Even a year after your original post, this information is still helpful. I was trying to wring a bit more life out of my old machine and bought a BFG 7800GS factory OC card. I was about to buy a new MB, memory, and processor to stop the artifacts , missing textures , warped polygons and overall graphic issues in Battlefield 2 and 2142. I stumbled on this post and as so many others have also done, managed to fix the problem thanks to this information.
Kudos to you for working this out, and sincere thanks for taking the time to post it. For reference, I have a SiS 645 chipset on my mobo.