The port that Remote Desktop uses is 3389.

This pertains  to remote desktop  in Windows.
 
The only port number  that remote desktop uses is 3389 & this is the only port you need to open in your firewall in order for remote desktop to work through a firewall.

Q. What port does Remote Desktop use? Does everything go over port 3389?
A. Port 3389 is the only port you need to open. Windows will attempt to stream sound through User Datagram Protocol (UDP) first. If no port is available for UDP, sound will stream through a virtual channel in Remote Desktop Protocol, which uses port 3389.

Pasted from <http://www.microsoft.com/windowsxp/using/mobility/rdfaq.mspx>