You'll be able to receive all the Free to Air (FTA) channels (free, unencrypted) without a viewing card. A viewing card is only necessary for the Free to View (FTV) channels (free, encrypted). Sky do a
"Freesat from Sky" viewing card (£25), which gives the FTV channels.
http://en.wikipedia.org/wiki/List_of...hannels_at_28E
http://en.wikipedia.org/wiki/Freesat...S_Viewing_Card
One thing to note though: You will
not be able to make use of the Sky+ box's actual Sky+ PVR features
without a Sky subscription for that box (e.g. Multiroom, to mirror the main box's subscription onto the 2nd box, or a Sky+ subscription, to simply give the 2nd box PVR abilities).