Not necessary with the LinkSys. ATT recognizes the MAC address of the NIC in the computer they originally installed to. When you set up the router, you just "clone" this address to it, plug in the cable modem, and bob's your uncle.
You just answered the question I was about to ask. Thank you! I know the cable company took the MAC address of the NIC on my XP computer. I was worried that if I got a router, I'd have to change the configuration through AT&T and get charged more money.
I will go to CompUSA tomorrow and look for this Linksys router. Otherwise I'll get it online. Thanks for all the help!