Something to try ...
Download and install Microsoft Installer cleanup utility, there are instructions on the page as well as the download. Note that what you download is the installer not the program – you have to run it to install the program.
To run the program – All Programs>>Windows Install Cleanup
http://support.microsoft.com/kb/290301/
Try uninstalling any instance of Apple software update.
If you get an uninstall failure, run the cleanup utility and remove any instance of Apple software update that you find.
Download the iTunes installer and save it on your desktop.
http://www.apple.com/itunes/download/
Rune the installer from there.
Message was edited by: polydorus