Depends on the source of your HDTV signals. For over-the-air, one popular solution is to use a satellite receiver box. In your case, if you've got digital cable and they offer the DVR, I'd use that since you get all the other advantages of the DVR in addition to just being able to tune in your HD channels. Otherwise, I don't think it much matters what type of device you use (as long as its HD compatable, of course!).
Cheers,
Kevin