This is probably written down somewhere, but I had to discover it myself, so I'm posting it again: I have one WRT54G (BOXA) plugged in to the internet. It has the default IP of 192.168.1.1. I have another WRT54G (BOXB) which I want to use as a client to connect some other computers to the internet. The problem is that from the factory BOXB has the same IP as BOXA, so if you plug a computer into BOXB, the packets can't get through to BOXA. The solution is simply to change the local IP address of BOXB from 192.168.1.1 to 192.168.0.1.