If you are still having issues with your iTunes in Vista after running the program with full admin privileges as suggested earlier, try getting the iTunes Repair Tool for Vista from Apple.
It can be downloaded here:
http://www.apple.com/support/downloads/itunesrepairtoolforvista10.html
For more info on it, check out apple's Knowledge Base here: http://docs.info.apple.com/article.html?artnum=305042




