So you have your DSL modem from AT&T, SBC Global, TDS, or other provider working on your PC directly and you want to set it up to work with your router (Linksys WRT54g / WRT54gl or other router) instead and can't find straight forward instructions on how to do this right?  Following these simple steps, we should be able to get your internet up and running through your router with relative ease.  The following steps are written for AT&T and a WRT54gl router, but should be similar with other DSL providers and different brands of routers.

1. Make sure that your phone line is connected to your modem
2. The ethernet cable from your modem is connected to the ethernet port (possibly labeled internet) on your router (it may also be a single port set aside from the others).
3. An ethernet cable from your router (a port labeled 1,2,3, or 4 possibly or choose one of the ports grouped together on the router) is connected to an ethernet port on your computer.
4. Make sure the router and modem are plugged into a power outlet and are powered on.
5. Open a browser (Firefox, Safari, Chrome, Opera, or Internet Explorer) and type in the address of your router if you know it. Common addresses are 192.168.0.1 or 192.168.0.2 or 192.168.1.1.  You may need to consult your routers documentation if you cannot find what the address is, but using one of the above address above, it is likely that you will be able to access your router unless this address has been changed by hand in the past.  You should get a window that will pop up asking for your login credentials when it connects!
6. (If you know your login credentials, enter them and skip this step!)  If this is the first time setting up your Linksys router, typing Username: "admin" and Password: "admin" may let you log in, otherwise please consult the documentation for your router for the default login credentials.
7. After you have logged into your router, there are a few settings that we'll want to change to get your router to work with your DSL modem. First, you will need to find the window with a drop down menu containing "Automatic Configuration - DHCP" or something very similar and make sure that it is set to that entry. Boxed RED in the illustration below.
   
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9.  Next, find a couple of input boxes labeled as or similar to "Local IP Address" with the values [192   168    ?     ? ] as boxed in RED in the illustration below and change them to [192] [168] [2  ] [1  ].  This is very important because the modem's address is likely configured to 192.168.1.1 which will cause the router and modem to get confused if they are the same and/or on the same sub network.  
10. Then make sure to save your changes (Probably a button labeled "Save" or "Save Changes") as boxed in GREEN in the illustration above. 
11. Wait about a minute, then unplug the power cable to your modem and your router and wait about another minute.
12. Plug the power cable back into your modem and wait for all of the lights to stop blinking and turn a solid color.
13. Plug the power cable back into your router and wait for the lights to stop blinking usually within 30 seconds or so.
14. At this step you can either restart your PC/Mac or if your using a PC (Windows 7 - May be different for Vista or XP) you can go to the Start Menu -> All Programs -> Accessories -> Command Prompt and type in "ipconfig /release" then type in "ipconfig /renew" and close the window down.
15. At this point whether you performed the release/renew commands or restarted your computer, you should be able to open up a browser and have access to the internet!

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