No, no you can't (there isn't any mobile media device that'll play full HD). 560px horizontal stuff is not HD ("full HD"/1080p is 1920px horizontal).

There's really no such thing as a 32bit screen. You mean 24bit.

What's to suck? It's a list of videos on the device that you double-tap to watch, and a text-box to enter a URL or filepath into. Realistically, most people would only spend about 1% of the time in the interface, and good, fast video playback is a lot more important than the stupid interface.

Besides, have you tried Mediabox?

Anyway, here's the straight dope: MPEG4/MP3 encoded avi files in the 400x240 (fit whatever dimension hits the limit first—320x240 for 4:3 stuff) pixel range at about 800-1500Kbps will play fine 100% of the time with mplayer. If you don't mind transcoding your stuff, then that's all you really need to know.

Personally, I have had a lot of success with stuff up into high 500-pixel horizontal range (I've even had some success with low 600-pixel horizontal stuff at 2.39:1) at about 700-1300Kbps (which is what most of the stuff you get from the "internet" is encoded in). It plays with just a hint of framedrop in high-action scenes. As some people find any framedrop unacceptable, you'll have to decide yourself if this is worth it.

h.264 can play, but only well at lower bitrates and resolutions (just as well, because the codec is particularly good at those sizes and bitrates). mplayer does not currently have good support for h.264, so you'd want to use Media player for that.

Again, personally, I find that the other features of the NITs greatly outweight any video issues for me. If you're looking for a strict media player, then this isn't really the device for you, but if you're looking to do just about anything (and everything) else, then the N810 is where it's at.

Now, one thing you might consider is a wait-and-see approach, as none of the mobile devices mentioned are particularly fresh at the moment, and updates should be forthcoming within the next 6 months or so. Nokia's next generation tablet (presumably the N900) will (almost certainly, as there's no hard evidence to support this yet) not have the video bandwidth and horsepower issues of the current generation tablets.