IIRC when I had BB installed at my old house the engineer ran a second cable (from the little connector box on the outside wall) up the outside of the house and ran it through the bedroom wall. I would imagine therefore that they should be able to do the same for you so you could keep your pooter downstairs.
I'm sure one of the NTL bods will be along shortly (well, maybe not that shortly - it is early after all
) to offer some better advice.