Depending on the brand and model of router that you have, it might be http accessable (meaning you can view it like a web page). Look up the instructions that came with it. If you are using DCHP on the router, it will most likely have an option to look up the client table, and there you should see your PC and Xbox IP addresses.
But I agree with everyone else. This is kind of a broad question to be covered in a chip manufacturer's forum. There are great basic networking tutorials all over the internet. Google is indeed your friend.