Hello MarkJennings,
Please see if the Uninstall tool below will help to remove iTunes and reinstall it. This would remove any corrupted files and let you install a clean version.
Diagnose and fix program installing and uninstalling problems automatically
http://support.microsoft.com/mats/Program_Install_and_Uninstall
Download iTunes from the link below:
http://www.apple.com/itunes/download/
Hope this helps.