I had the same thing setting up my 555 the other week, if you need a model number its DSI 8215. It's on the bottom of the HD box. I didn't get a sky hd box option either
There are a couple of other routes to get it.. Last time I tried it you could select Manufacturer Sky, Model SkyHD.. but I suspect that was a glitch since Sky isn't a manufacturer.
Another way is just to tell it you have the remote and fire a couple of keys at it, so it's able to do the search itself.