check the file properties on the mstsc.exe (c:\windows\system32\) and check the details tab and check the version (may be under version tab depending upon OS) or run mstsc.exe, right click on the icon in the top left hand corner and select about.
This shows the valid command line switches
http://blogs.msdn.com/b/rds/archive/2007/12/17/changes-to-remote-administration-in-windows-server-2008.aspxHope this helps
