If you are thinking about "how would a cracker map my network" you can do several things...
If the router allows login connections, they could try to get into your router and look at the routing logs to see what it is connected to.
If it has firewalling, they could use "firewalking" techniques to map the network.
(do a google search for the word "firewalk" or it may be listed in the "Top 50 Hacking Tools" at insecure.org)
There are other techniques I'm sure, but these seem to be the easiest (in my eyes.) Maybe some other people have some other ideas. Hope I've helped. Have fun.
Happy Hacking
