The IP is the IP to your computer. Often, this is 192.168.1.1 or 192.168.1.2 or something along those lines, but can vary depending on how you have your router set up and the number of computers connected. You can find out your IP be going to your start menu and running CMD (from Run in XP or by typing it into the box in Vista or 7). Then, in the command window, type ipconfig and it will give you your correct IP to use.
Check
http://www.portforward.com/ for additional help setting up ports on your brand of router.