If mazolauk uses a standalone modem, there is no need to register the new PC - all that is required is a reboot of the modem.
If he uses an STB, then the MAC address of the PC will need to be registered by sending his web browser to "start.ntl"
http://homepage.ntlworld.com/robin.d...tips/swap.html
http://homepage.ntlworld.com/robin.d...r.html#pacereg