Set RDP Client to Listen on a Specific Port

On the client, add the port # to the IP address of the server
you are attaching to...

%REMOTESERVERIP%:%PORT#%
http://support.microsoft.com/kb/304304

On the server, change...

HKEY_LOCAL_MACHINE\System\CurrentControlSet\Control\TerminalServer\WinStations\RDP-Tcp\PortNumber
to the port you desire.
http://support.microsoft.com/kb/306759