You can't receive HD channels from the cable co. with a DIRECTV HD receiver. You have to use a box from your cable co. because only their box can decode their digital signal. The cablr co. uses a different encryption than DIRECTV. You can buy an HD decoder if your tv doesn't have one built in and hook up an off air antenna to receive your local channels in HD.
This is CABL.com posting #131206. Tiny Link: cabl.co/mIio