It's probably best if I start by explaining the difference between Freeview, Free-to-Air and FreeSat:
Freeview is a company (jointly owned by the BBC, ITV, BSkyB and the transmitter owners) which broadcasts a collection of channels via terrestrial TV. To receive Freeview, you need a good quality (terrestrial) aerial and a Freeview digibox. A Sky box won't work. (Freeview is not available via satellite).
Some satellite channels are 'Free to air'. These channels can be received by anyone who's got a properly positioned satellite dish and any (satellite) digibox. Your Sky digibox should be able to receive these signals.
FreeSat is the name of a non-subscription service provided by Sky. It's similar to Freeview, but the selection of channels is not identical. Although no subscription is required, peope without existing satellite equipment have to pay �150 for installation.
People who already have digital satellite eqipment need to purchase a FreeSat card, for �20, from Sky. That's because, unlike Free-to-air transmissions, Freesat channels are encrypted.
For confirmation of that last paragraph, scroll down to "I already have digital satellite equipment:, here:
http://www.freesatfromsky.com/?pID=6
For further information, including a list of free-to-air channels, see here:
http://www.wickonline.com/fta.htm
Chris