1. Hit the 'Windows' and 'F' keys on the keyboard simultaneously to bring up the Search window. Search for 'QuickTimeInstaller.exe' and 'iTunesSetup.exe,' without the quotes. Delete all copies of both files.
2. Open Internet Explorer. In this window, click 'Tools,' then click 'Internet Options.' Click the 'General' tab. Under the 'Browsing history' category, click the 'Delete' button. This removes all of the temporary files Internet Explorer saved, and may take several minutes on slower computers.

3. Close Internet Explorer and then reopen it. Browse to the iTunes website and download a new copy of iTunes. The copy should install without any difficulty.