More runas examples

Computer Management with administrative credentials
runas /user: ComputerName \administrator "mmc %windir%\system32\compmgmt.msc"

Active Directory Users and Computers with domain administrative credentials
runas /user: DomainName \administrator "mmc %windir%\system32\dsa.msc"

Active Directory Users and Computers in another forest
runas /netonly /user: DomainName \ UserName "mmc %windir%\system32\dsa.msc"

Source: http://technet.microsoft.com/en-us/library/cc781769(WS.10).aspx