Tweaking.com - Remote Desktop IP Monitor & Blocker is a free tool to monitor any IP that tries to connect to the remote desktop. From the author of Windows Repair.
This free program will monitor the remote desktop port using the Windows netstat API and keep them in a log for later viewing. The program has a built-in block IP tool to easily block any IP address. It does this by using the built-in Windows IP Security Policy (IPSec).