Need help upgrading iTunes, PLEASE!!

I'm trying to upgrade iTunes and keep getting an error message that says something to the effect of "iTunes does not have enough privileges to access the file MyComputer/ProgramFiles/ITunes. Please log in as the administrator or notify your system administrator." I am the administrator!! No one else uses my computer and I'm not on a network. I've tried completely removing my older version of iTunes using Add/Delete, but it didn't help. I've tried reinstalling much older versions of iTunes but got the same error message. Any ideas/tips? Help? Please?