Yes, but you'll need to phone Sky and get them to pair your viewing card to the HD box - at which point they'll try and push an HD subscription,but just tell them your not interested and just want the card paired!
In addition to all the channels you get from your current Sky+ box/subscription ,the HD box will also give you access to BBC HD, ITV1 HD, C4 HD, Five HD, Luxe TV HD and BBC1 HD (when it launches) as these are all FTA (Free To Air) or FTV (Free To View) channels.