Don't have instructions on how to hook it up. i have cable service through an external modem.

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I will try to make this as clear as possible, but if you have any questions, please come back here and let me know.

You will need 3 things: Modem, Wrt54G, computer. Put them next to each other without having plugged in anything (no Ethernet, no power cable!). Make sure that the WRT54G router is back to default settings by pressing the reset button on the back of the router for 10 seconds while it is powered on.

1. Connect the power cable to the Modem. Power light on?
2. Connect the power cable to the router and wait until the power light is on steady.
3. Connect your modem to the router. Plug an Ethernet cable first into the modem and THEN into the WAN port (the label says "Internet") of the router.
4. Plug an Ethernet cable into one of the router LAN ports and connect it to your computer.
5. Power on the computer.
6. Open the Control panel and the Network Connections applet.
7. You should see something called "Local Area Connection".
8. Double-click on it and click the Properties button.
9. Double-click on "Internet Protocol (TCP/IP)" and make sure both radio buttons are set to "Obtain...automatically".
10. Close all Windows by clicking "OK".(The second one takes a moment, because it applies the settings.)
11. In the open window choose the Support tab and you should see your IP address, your Default Gateway (192.168.1.1) and your DHCP server (192.168.1.1)
12. Open Internet Explorer and type "192.168.1.1" in the address bar.
13. If you had reset your router to factory defaults, leave the username blank and type "admin" in the password field.
14. On the first page (Setup), you should set the Internet Connection Type to "DHCP" (if you have a cable connection), unless you get a static IP from comcast (which I doubt). Here you might have to choose PPPoE, if you are using DSL.
    
15. Go to the Wireless tab and ensure that wireless is enabled.
16. Go to the "Security Tab - Wireless Security" and ensure that NO security is enabled for now.
17. Open a new browser window and see if you can open a web page. Use an address that is unlikely to be in cache - try "http://www.mit.edu" or so.
18. Close your browser for now and come back here later to setup your wireless security etc.
19. If you were successful - sit back for a moment, enjoy the triumph and treat yourself with a nice drink!

There are a couple of things you still have to do, but the main thing is done.

1. Make sure that you can access the internet from your wireless laptop before you start changing settings.
2. Get a manual for the router here.
3. Go back to your router's web page and set up wireless security (don't use WEP - that is not secure enough)
4. Once you're up and running and feel familiar with the settings for your router, I would change to a different firmware, because I never was really satisfied with the Linksys firmware. I use tomato, for the simple reason that I was afraid of other more complicated firmware and you can always go back to Linksys, of you don't like it.

So...my fingers are bleeding now, but I hope this helped you out.
If so, please come back and let me know. Others might have a similar question.
If not, just tell me where you got stuck and we will go from there. According to the movie 'Galaxy Quest':
"Never give up, never surrender!"