I have the same condition as yours. The connection Now TV is there must have a boardband modem in your Living area and the boardband cable is from the Tel. line to the Now Decoder through the modem and they will using AV lines (Red, Black and Yellow) from the decoder to your TV or any AV centre. The Cable TV is from the antienna to the cable TV decoder then to your TV's antienna. They are totally seperate.
However, one thing you have to consider is the location of the boardband modem. If you installed in your living area, you have to use a wireless router to share and transfer to the your room, which you place your computer for internet. According to this reason, I installed the modem in my room and have not connect the Now TV for more than one year.