If your trying to limit users from accessing your machine via RDP, I would start with the basics and simply disable Remote Desktop.
My Computer > Control Panel > System > Remote
Second, I would use the netstat -a command that toddwoo suggested. Then you can identify if a port is open and trying to listen via RDP.
Finally, I would configure your firewall to block RDP traffic. The default port for RDP is 3389. But keep in mind, one can change the listening port for Remote Desktop by a simple edit of the registry.