Go to Microsoft website to fix install and Unistall problems. Click "Run now" from Fix it to remove all iTunes & related installer files:
http://support.microsoft.com/mats/Program_Install_and_Uninstall
Be aware that Windows Installer CleanUp Utility will not remove the actual program from your computer. However, it will remove the installation files so that you can start the installation, upgrade, or uninstall over.