Have a look at this
http://homepage.ntlworld.com/robin.d...r.html#pacereg
You need to get the MAC address of the Router allocated to the STB. Plug it in, power cycle the STB, then the Router, then the PC and you should be able to access.
http://start.ntl or
https://autoreg.autoregister.net/start.html
ntl-ct8-cb487 is the serial number you might need, you will also need your UID and PW from the welcome letter(s).
Once the router is registered it should all be fine.
I assume this is a wired only router? If not do all the set up wired then once you can surf wired setting up the wireless is another step.