The free service from Sky is called "Freesat from Sky" and you can read more about it on the link below.
You can buy the dish and box from them, but it does cost £175 (but then no montly charge).
But I believe if you just buy any Sky box (from ebay) and connect it to the dish you automatically get all the free channels.
Sky talk about a £25 fee for a card, but I am not sure how important that card is or if it works without it (see the FAQ on the link below for more about the card)
http://www.sky.com/shop/freesat/home/