[Paul]

The mac address is how NTL authenticates the connected equipment on the account. Normally just power cycling the equipment when connecting it would suffice to get everything registered properly but with wireless it can be a bit more work.
To clone the MAC address I would get the wired connection working, do an ipconfig /all and get the MAC/ physical address of the working connection. Then clone this MAC address into the router so that the cable modem sees this MAC address when it looks at the router.