There are two HD PVR boxes from Technomate, the 6900 and 6800. The 6900 has a satellite tuner and a Freeview tuner, with the 6800 possessing the satellite tuner only. Both are able to record HD broadcasts (and SD) if you add a hard disk via USB2. You can then transfer your recordings to a PC for archiving if you wish (something you can't do with Sky). You don't get a satellite EPG like Sky, however, only 'now and next'. There's also a new box from Topfield (TF7710) which has 2 satellite tuners and a hard disk already built-in. This box has the advantage of being able to record two channels at once (or record from one channel and watch another at the same time), but I'm not sure whether it allows you to off-load your recordings to a PC- it's manual appears a bit vague on this matter. All of these boxes will receive the free to air HD channels (as well as the SD ones of course), but I'm not familiar enough with them to know whether you can use an existing Sky card with them.
AFAIK, you will need a particular CAM, and I believe that you will will need to place the card back within an Sky box every so often to keep the card 'active' as it were. I'm no expert on card matters (I'm only interested in free to air stuff myself), but others on the forums should be able to advise you.
There should be more HD PVR models by Spring when the BBC / ITV/ C4 / C5 freesat service launches.