EDTV is Enhanced Definition and can only display 480P, standard definition, not high definition. The ED displays can accept an HD signal, 720P or 1080i, but will down downconvert to 480P. They produce a nice picture but are not HD and unless you can buy one for under $1500.00 why bother? Your money is better spent on a true HD set whether it be LCD, Plasma, DLP or LcOS.
High Definition is either 720P or 1080i.
HDMI is High Definition multi Interface which is an upgrade of DVI, Digital Visual Interface. HDMI can transmit both video and audio digital signals. DVI can only transmit digital video.