Moonstruck
So after a certain amount1 of fiddling it seems its possible to play videos on a DS. You need a copy of Moonshell, which you can get here , and, in my case a Datel Max Media Dock and a compact flash card. Install Moonshell to the card, encode your .avi files to .dpg (using dpgtools which you can download at the same time as Moonshell), play the resulting .dpg file. The interface is minimalist2 but straightforward and now that movies are happily playing in the top screen, I'm wondering what you could use the touchscreen for. Marking up interesting shots? Drawing moustaches to stick onto the actors?
Here's a thing though. If I put the DS down on a flat surface with the dock in place, with the console open, it promptly keels backwards. Now since I stopped dripping vodka into its GBA port last week, it has no excuse for such behaiviour and I've had to have stern words with it. Frankly, it's letting the side down. As with so many3 of the problems in my life, I find that rubber feet are the answer.
1 a hell of a lot
2 deeply ugly
3 almost none