[MovedGoalPosts]

Based on the setup you posted at the beginning, all you should need to do is replace the ADSL connection with the new ntl connection. You already have the internet connection sharing system setup between your own and your childrens PC, and that arrangement can continue. You might have to rerun the internet connection wizard just the once though, to ensure any new settings specific to ntl are imported.

Of course you do not have to use the modem/STB to USB connection, you can add a second ethernet card to your main PC very cheaply.