I was thinking about purchasing a Zenith HDV420 for a good price from a friend. 1) What can I do w/ it that I can't w/ Comcast HD service besides pull in a few more channels? Is it possible to pull in more premium channels? 2) I already receive FOX-HD, CBS-HD, NBC-HD, INHD 1/2, ESPN-HD, and HBO-HD via Comcast. With a HD-set top box, I can get UPN-HD, WB-HD, ABC-HD, and TBS-HD.