Mark Russinovich from Microsoft developed a tool as part of Sysinternals to give you the “Run as…” option when you right click a program in Vista. Without this tool, Vista will allow you to run as Administrator, which is totally useless when you’re trying to access a domain resource.

Once you unzip “shellrunas.exe” (put it somewhere in your PATH) you will need to run “shellrunas /reg” at a command prompt. Once it tells you it has been registered, you will see “Run as different user…” in your right click menu.

The link: http://technet.microsoft.com/en-us/sysinternals/cc300361.aspx