How do you set up internet on a linksys router?

I have an RCA Modem and a Linksys router WRT54G. I got the router working, it is sending a signal, but I think the IP adress is not programmed onto the router because I cannot connect to the internet.How do you set up internet on a linksys router?
I hate setting up routers for the first time because the instructions didn't help me at all and neither did customer support. When you are installing the router and it says please wait while we check your internet connection settings, reset your modem. As soon as it starts checking connection settings reset it. Work everytime for me.