MAC Address and Ethx

[Bob Underwood <mgkrebs1@home.com>]

I had a phone call from my Cable ISP the other day, stating that I should 
reconfigure my computer or risk losing connectivity.  The web site they 
pointed me to is a windows site, basic config stuff.  Later phone call to 
tech service (level one and level two) confirms they are going to start 
checking the MAC addy of the modem as opposed to my previous @home username, 
etc.  Level one actually told me that my choices are to either find a new ISP 
or use windows.

Is there a way to pass the modem MAC address along to the network in the 
ifconfig?  If so, how would I do that?

TIA

Bob