Just some info I've found...
The Dell 20" wide screen LCD uses the same panel as the Apple 20" cinema display, except it has more inputs, a brighter backlight, and is way cheaper.
For
High Def, you will need:
16:9 (the rectangle displays... square displays are 4:3)
1280x720 or 1920x1080 (or higher)
"p" as in 720p or 1080p is better than "i" as in 720i or 1080i
I don't think there is any consumer level screen that does 1080p. The displays themselves can do it, but the electronics can't.
In the Wikipedia article, mentions that "HDTV" programming is either 720p or 1080i right now. 
