if you are still having problems installing iTunes try this solution that I used for a family member having the same error:
go to start>>control panel>>user accounts >>create a new user account that has admin
in the new user account try to install iTunes for all users.
If it installs, log out and go to your usual account, check you have access to iTunes and can use the program, set it to find your music and create the library.
Once your happy its installed and fully working you can delete the spare user account that you made.