Nick and Bill are correct. The card is only required for certain channels BUT not BBC/ITV/CH4/Five.
Depending on the card/digibox sometimes you have to add in Five and ITV. This gives the impression you need a card... details here on how to add channels see here: - http://uk.answers.yahoo.com/question/index?qid=20081127135606AAftoUC
For a full list of Sky/Astra/28.2e channels go here: - http://www.wildsat.com/astra.htm