That is just the beauty of it :)
Using NAT the IP is translated back to the client machine by the router. You just see the IP of that router that is also working as a basic firewall. But why would you need to know that address? It is useless when you are not a part of that same NAT. The IP of that machine will be 192.168.1.x like so many other machines but it isn't an IP you can use to trace back the machine over Internet. But you also wouldn't need it though.
http://en.wikipedia.org/wiki/Network_address_translation[
^]
Good luck!
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