I'd like to take my Freeview signal (or it might be satellite or anything else with a Scart connection) and pump it round the house on the coax on a spare channel. I understand this is simple and cheap enough to do but I could use it being spelt out for me. So:

1) I guess I'll need a modulator - what type?
2) Where does the output have to be fed into - presumably the aerial distribution point? How does it combine with the existing signal from the aerial?
3) Is there a way of running the output back up the existing cabling or do I have to put a new run in?

Sorry, I know these are dumbass questions but with a few basics I can usually get up and running quick enough.

Also, I'm thinking about using a transceiver to send a coax based signal over Cat5 (for CCTV but I guess it could apply to the Freeview). Is this a lot more aggravation, ie cost than putting in coax runs?