If you are trying to connect to your Cisco Router G Broadband WRT54G, you’ve got to hit http://192.168.1.1 in your browser. You could hit it from this post even. So that’ll take you to the UI, but first you’ll be prompted by a password. If you never changed the defaults, they are:
That’s for Cisco Router G Broadband Router WRT54G Firmware Version: v2.02.7.
Then, once you are in, you can change things like the security key., etc.