On Error Resume Next
Set wshShell = WScript.CreateObject( "WScript.Shell" )
strUserDomain = wshShell.ExpandEnvironmentStrings( "%USERDOMAIN%" )

strComputer = "."
Set objWMIService = GetObject("winmgmts:" _
    & "{impersonationLevel=impersonate}!\\" & strComputer & "\root\cimv2")

Set colItems = objWMIService.ExecQuery("SELECT ClientSiteName FROM Win32_NTDomain WHERE DomainName = '"& strUserDomain &"'",,48)

For Each objItem in colItems
  ' Hier wird der erkannte Sitename der Anmeldedomäne ausgegeben.
  strSiteName = objItem.ClientSiteName
next

select case strSiteName
	case "Berlin"
             ' Tu irgendwas
	case "München"
             ' Tu irgendwas anderes
end select

Getestet unter Windows XP, Windows 2003, Vista und Windows 7.