They started rolling out HDTV several months ago up here near Philly. Yes, you must have a decoder, and Comcast will 'lease' you one. I think they use the Motorola DCT5100. It has component output, so if you have your HDTV setup right, you can get the 1080 resolution. Otherwise you could connect the S-Video and get 500 lines resolutions, basically double the 250 you get with standard coax.