Does your computer have Vista on it? If so, did you install the game in the default installtion location under "Program Files"? If so, then remove the game from your computer and install it in another folder besides "Program Files".
Vista messes with everything in that folder all the time. Even when you disable UAC, it still is messing with it causing performance issues.
If you do not want to do that, then read
this. The section about "where are my files" is what you want. Vista redirects files creation for programs installed in the "Program Files" folder.