When installing iTunes for Windows on a Windows Vista or Windows 7 system, you receive the following error message:
The administrator has set policies to prevent this installation
... even though no such policy has been set on the system in question.
Usually, the message seems to indicate that a permission on a file, folder or registry key has gone awry for the Windows user account in which you're installing iTunes for Windows. If that's what is afoot, running the install using the Administrators group's permissions can get iTunes for Windows installed.
Download and save a copy of an iTunesSetup.exe (32-bit iTunes for Windows installer file) or iTunes64Setup.exe (64-bit iTunes for Windows installer file) to your hard drive. (Don't run the install on line and don't start the install just yet.)
Now right-click on the iTunesSetup.exe (or iTunes64Setup.exe) that you downloaded and select "Run as administrator".