ShellRunas is free utility from Microsoft that integrates into the Windows context menu to launch programs as a different user. It provides similar functionality to that of the command line based RunAs utility.
ShellRunas works on Windows XP, Windows Server 2003, Windows Vista, and Windows Server 2008, and is created by Mark Russinovich of Sysinternals fame.
You’ll have to run shellrunas.exe /reg from the directory you extracted the shellrunas.zip file to in order to add the Run as Different User option to the Windows context menu.
Once shellrunas.exe has been registered and you select Run as Different User from the context menu, a dialog box similar to the one shown below will prompt you for alternate account credentials.