Another extremely easy to use & setup remote X login system is called VNC. You can find it at http://www.realvnc.com/
It allows you to login to any PC running a VNC server from anywhere in the world as long as the client can access the servers IP number via the Internet, over a LAN, etc... It starts an X session just like you were sitting at the server's terminal. There is also a Windows version of the client so you can log on to your Linux box from a Windows box.
I think this is what you are wanting to use XMDCP for. I have never encountered a program as simple to setup & use as this one. It is excellent! I would highly recommend you give it a go!
Post back here & let me know how you found it.