Contrary to other eBay guides, SKY Cards DO work in any box to view Free To View channels. Yes, to purchase movies (ppv), include any premium channels like Sky Sports or Sky One you will need a Sky subscription and matched box and card. And yes, anyone that says you will get these channels with the card is a scammer.
However active Sky Cards will allow viewing of all Free To Air (FTA) and Free To View (FTV) channels in any set top box, including BBC 1, 2, 3 and 4 (with all regional variations), ITV 1, 2, 3 and 4, the new Film 4 and Film 4+1 movie channels, Men and Motors, BBC News, Sky News, CBBC CBeebies and over 200 digital radio channels. (Google "Free To View" channel listing for a full list!).
This is also know as a Freesat system, which can be purchased and installed for around £150 but if you already have a unused dish and Sky Digibox then getting a card is a very cheap way to get all the new Digital channels and "Red Button" features.