Not sure I can help with all your questions, but here goes.

We have broadband cable coming into the house that's fed into the back of a router that clones the MAC address that the cable company recognises. Therefore any computer plugged into the router has instant access courtesy of the cloned address.

It all works really well, although I have no idea how to split the TV/internet cable. We have a Telewest box on the wall out of which comes the two separate cables.

It's worth it though, so keep perservering. Good luck!