Microsoft Update is an optional service that updates both Windows operating systems and other Microsoft products, as apposed to Windows Update which only updates Windows operating systems.
When I visited http://update.microsoft.com/windowsupdate/v6/default.aspx on a computer that uses Windows Update, I was able to download and install the Microsoft Update software.
Once installed, clicking on the Windows Update shortcut, %SystemRoot%\system32\wupdmgr.exe, brings you to the Microsoft Update Web site.
NOTE: The Microsoft Update shortcut uses the %SystemRoot%\system32\rundll32.exe C:\WINDOWS\system32\muweb.dll,LaunchMUSite target.
NOTE: Once Microsoft Update is installed, you may delete the Windows Update shortcuts.