I connect to my high-speed DSL Internet service using a Westell WireSpeed modem that's hooked up to a Linksys WRT54G router. Last week a power outage hosed the settings on the modem and router, which knocked me offline until I figured out the proper configuration. I was so desperate at one point that I called my ISP's outsourced tech support, speaking for 15 minutes to a pleasant wage slave in Bangalore or another distant port o' call center who could not have been less helpful.
For the help of others in my predicament, and myself in the future when I forget how to do this again, I'm documenting how to configure a Westell modem to work with a WRT54G router.
First, connect a computer directly to the Westell modem using an Ethernet cable and see if you can browse the web. If you can, this confirms that your Internet connection is fine and your modem/router configuration is the most likely cause of the problem.
While the modem is connected, load the address http://192.168.1.254 in your browser, which opens a web application in the modem that enables it to be configured. Choose Expert Mode from the main menu, which adds options to the menu, then choose the Configure Connection option.
Westell modems are set up by default to act as their own router. This is ungood if you have another router, because they conflict with each other and neither works properly. When you are connecting the modem to a router, the modem must be set to "Bridged Ethernet" mode to disable its routing capabilities. This option can be selected in the Protocol drop-down box. After setting the modem to Bridged Ethernet, click Save and Restart Connection.
Next, disconnect the computer from the modem and turn the router and computer off, which for the router requires pulling the cord out of the back. Once this is done, plug the modem into the router with an Ethernet cable while the router's power is still off. Wait 10 Mississippis, then turn the router and computer back on in that order.
Load the address http://192.168.1.1 in your browser to open the router's web configuration application. This application requires a username and password. If you've never set one up, leave the username blank and use the default password "admin". The Basic Setup form is displayed. Choose the Internet Connection Type PPPoE (Point-to-Point Protocol over Ethernet), then click Save Settings.
To see if it works, choose the Status tab to display information about your connection. If Login Status is "Connected", the router's connecting to the Internet successfully through the modem. If not, click the Connect button.
(At this point you're done, but if you haven't set up router and wireless password, anyone can change your configuration and use your wireless Internet connection. Click the Administration tab to set a router username and password. Click the Wireless tab and the Wireless Security link to restrict wireless access.)
Broadband Reports has more information on configuring Westell modems and Linksys routers.