Well you answered my question enough. Sometimes two 128M sticks not matching ( IE: PNY - Kingston ) or more so Nano speeds unequal, can cause err in processing large files.
I read what you said, And I just don't feel it is your VideoCard because I am assuming you play other games of lesser and greater complexity and you stated that it was JUST this one game.
I either first thought it might be mis-matched MEM, and second you could just very well have a flaw on the CD that is to say a scratch or something that would cause it to not appear to be the same spot in the game everytime ... but can be the same spot on the CD.
Do me a thought. Uninstall it completely, drag the whole CD to your harddrive, reinstall it from there, and see if it still happens!