Windows Installer CleanUp Utility

If you find yourself having installation problems with a Windows application like a friend of mine had recently, where he couldn't install Microsoft Office Service Pack 3, but he couldn't uninstall the Microsoft Office 2003 either (in fairness, not due to Microsoft's fault, but to "mysterious" disappearing of %WINDIR%\Installer folder - that's what he says anyway :-), you can use the Windows Installer Clean Up utility to remove the application installer information so you can start over and re-install the offending application.

Description of the Windows Installer CleanUp Utility
http://support.microsoft.com/kb/290301

Download the Windows Installer Cleanup Utility package
http://download.microsoft.com/download/e/9/d/e9d80355-7ab4-45b8-80e8-983a48d5e1bd/msicuu2.exe