As far as i know all ntl STB's have scart sockets that can be set to RGB. As for audio, the most modern Samsung box doesnt have phono out plugs, but you can get SCART leads that have phone break out. Many ntl installers may even have these on their van, and if asked nicely can supply instead of a standard SCART lead.
It depends on the area in which you live whether broadband is supplied via the STB or a separate Cable Modem. When the engineers do the install, you can show them where you will want the box and any separate modmen to be (if you get a separate modem), otherwise, only where one the one ntl connection cable can be put. You can ask them to run the lead a little longer than strictly needed to allow for your future alterations.
If you do want TV in one room and Broadband in another, make sure that ntl's sales team re aware of this prior to the install so the engineers have the right kit with them.
Top tip, offering tea or coffee at an early stage will get you more co-operation from the installers
It's not a practical proposition to keep moving the STB and / or modem from one connectin to the other (if nothing else plugging in unpluggin is pain). Frequently you'll end up with connectivity issues.
Co-axial cable for a TV aerial or FM aerial is often of differing quality to that used for cable connections from the street. You can get signal loss or interference if the cables aren't adequately sheilded. The cables usually run by the ntl installers will be from the road to a box on the outside of your house, and then from that box, to the points of connection of a STB / modem.
They don't usually run cables within the house from where you would put your STB, to allow a connection to a TV in another room, your TV is assumed to be next to the STB. Ntl would expect you to have a second STB if you want to watch TV in two different rooms using cable. There are wasy around this. You can run your own coaxial aerial cable from the STB, or there are wireless solutions.