Active Ports bruger jeg selv og det er et lækkert program ;o)
From the developer: "Active Ports - easy to use tool for Windows NT/2000/XP that enables you to monitor all open TCP/IP and UDP ports on the local computer. Active Ports maps ports to the owning application so you can watch which process has opened which port. It also displays a local and remote IP address for each connection and allows you to terminate the owning process. Active Ports can help you to detect trojans and other malicious programs."
http://download.com.com/3000-2085-10121832.html?tag=lst-0-1