This week's book giveaway is in the OCPJP forum. We're giving away four copies of OCA/OCP Java SE 7 Programmer I & II Study Guide and have Kathy Sierra & Bert Bates on-line! See this thread for details.
Run netstat command on the command line. It will tell you which application is listening on which ports. I think the parameters to netstat change based on OS, although I might be wrong there. Look at the help for netstat