>If it's keyed to a MAC address, was it previously used with a different
>one, so that you need to reset or power-cycle the modem to clear the
>association, or perhaps even call the ISP and tell them the new address?
>
>  
>
Most likely this is keyed to MAC adress, what you do is take your own, 
or the one that your router/PC that you're using now to access the 
internet. Then, Under Interfaces: WAN put the MAC address of the 
machine/router that you are currently using into there. I've heard of 
MAC spoofers that claim 'Instead of changing IP, or to use a diffrent 
computer not being able to access the internet, spoof your MAC and 
you're set' There are many ways to find out what MAC you have.
To find out your current IP address or your router's IP address easily 
use this : 
http://www.astalavista.com/index.php?section=dir&cmd=file&id=686 .
Anthony Brohan