Router Woes

I currently am using a D-Link DI-524 that can no longer emit a Wireless Signal 3 yards or more.
After some researching, I purchased a LinkSYS WRT54GL. I want to get Tomato up and running, and up my wifi output frequency so the problems I had before wouldn't happen again. Here's the problem...

Upon trying to install the new router (the linksys), all lights light up as it should, but nothing can connect to the internet. My computer gives me Page not found in Firefox (via ethernet cable), my IPhone states that Safari is not connected to the Internet, and my PSP tells me that an Internet Test failed. The setup is identical to my last one, yet I can't get the router to work. I set up my old one, for the time being, and it works, as I am able to visit and post here.
Any suggestions? Its probably something I overlooked, but this router comes with no manual.

When you installed the new router did you turn off everything that was connected to it including the modem?
I know that the network addresses can be different depending on the maker. Some use 192.168.0.x others use 192.168.1.x.