if you're on a private net, or behind a firewall your computer could be using an IP that is private (10.X.X.X, or 192.X.X.X..), or you could be surfing through one public ip assigned to your router or other device..
You can certainly run wipipcfg on WinXp, or open a command prompt (start, run, cmd) and type ipconfig. If you are using a private number (see above) you can go to a site like http://www.grc.com
(not urle'd on purpose) to see your ip address (GRC: shields up to run the port test and to see what IP you are using).
I know the problem has been solved already...