Well, there are a couple of different ways to phrase the new forms of TV available.
Progressive scan means that it is regular TV with no interlacing (640x480 Non-Interlaced). But in HDTV speak that is 480p (640x480 Progressive scan). Regular TV is called 480i (640x480 Interlaced) or NTSC, or SDTV (Standard Definition Television I think).
There are 2 other major resolutions for HDTV and those are 720p (1280x720 Progressive scan), and 1080i (1920x1080 Interlaced).
For DVDs there is an extra thing that needs to be done to display DVDs in 480p and that is called 3:2 Pulldown. Basically what that means is that when films are transferred from 35mm to a DVD they perform a process on the picture to make it interlaced. 3:2 Pulldown simply reverses that process so the picture isn't interlaced anymore and is then displayed on the screen.
Therefore according to the X-Box's cardboard box if the unit can play movies (assuming they mean DVD) in HDTV it would need to be able to be a progressive scan DVD player. Now this contradicts all the reports we've heard so it may be an error on the box, or it maybe a preview of things to come.
Anyways, I hope this clears up any confusion with all the differences in terminology and resolutions for HDTV
