To watch HD, you need 2 things - first, a HD TV (which you've got). Second, a HD source to feed into the TV. A Sky+ Box is not a HD source (but you can still watch TV from it in normal definition). A Sky HD box is a HD source, though only certain channels are broadcast as HD (although you can still watch the others in normal definition). Several other things are HD sources - for example, a BluRay player, some games machines (PS3, Xbox, etc) , some computers, and a few other devices.