Tunneling via Putty is quite well documented. In Putty (the link points to the lastest version), create a new session.
In the SSH section, make sure compression is enabled (for SSH v2 – you shouldn’t be using anything earlier, anyway).
In the SSH=>Tunnel section , set the Source port to 127.0.0.2:3389, and the target to SERVER:3389 (where SERVER corresponds to your upstream Windows Terminal Server).
Once the connection has been created, and you’ve logged into the Putty session, connect to 127.0.0.2 on the local machine and you should be prompted by the remote machine.
This is all as a result of the “localhost” restriction in RDP sessions – however, there is a patch.
Simple as π