This is my setup:
Connect existing aerial cable to output port on Sky box.
Other end of aerial cable plugs into a distribution unit in the loft.
From the distribution unit I can connect other cables going to any rooms (I have 2 others using aerial cables that were already installed)
What you are watching on the 'main' telly is pushed throuout the house and you use 'magic eyes' in the other rooms to control the sky box remotely.
Our maintelly has freeview built in so we can watch anythning freeview on that while the kids watch sky channels on the other telly if required.
Works well and cheap/easy to set up.
Sky box only outputs standard definition even on HD boxes.