If you type runas /? at the commnand prompt it will show you the options. One of them is user:mycahine\administrator ;\)

H:\>runas /?

RUNAS [ [/noprofile | /profile] [/env] [/netonly] ]
        /user:<UserName> program

RUNAS [ [/noprofile | /profile] [/env] [/netonly] ]
        /smartcard [/user:<UserName>] program

   /noprofile        specifies that the user's profile should not be loaded.
                     This causes the application to load more quickly, but
                     can cause some applications to malfunction.
   /profile          specifies that the user's profile should be loaded.
                     This is the default.
   /env              to use current environment instead of user's.
   /netonly          use if the credentials specified are for remote
                     access only.
   /savecred         to use credentials previously saved by the user.
                     This option is not available on Windows XP Home Edition
                     and will be ignored.
   /smartcard        use if the credentials are to be supplied from a
   /user             <UserName> should be in form USER@DOMAIN or DOMAIN\USER
   program         command line for EXE.  See below for examples

> runas /noprofile /user:mymachine\administrator cmd
> runas /profile /env /user:mydomain\admin "mmc %windir%\system32\dsa.msc"
> runas /env /user:user@domain.microsoft.com "notepad \"my file.txt\""

NOTE:  Enter user's password only when prompted.
NOTE:  USER@DOMAIN is not compatible with /netonly.
NOTE:  /profile is not compatible with /netonly.

- Chuck Norris once sold ebay to ebay on ebay.