The DVDs I've seen so far with ATSC tuners and HDMI outputs can all forward HDTV content to your TV at the resolution it is broadcast in. They cannot RECORD that high definition, but will record a downsized version of it onto a DVD. No harder than DirecTV HD receiver sending HD content to your TV through HDMI or Component while sending an SD version of that programming through Svideo and composite outputs.

I've been reseaching how to make an Xbox 360 HD-DVD drive play HD-DVDs on my PC and came across some suggestions that there is a standard DVD format of HD programming that can be played by some of these HDMI endowed DVD players. Not enough info to know what that's all about, though.