As I developer that used to write games for 8 bit machiness, I've been interested and looking around to develop some bits and pieces for my DS.
Anyway, I'm using the techniques used in the following article. Really good stuff for anyone interested in developing some homebrew games or solutions for their DS.
http://www.double.co.nz/nintendo_ds/index.html
The official DS development SDK is a bit more difficult to obtain, as you need to have an official license form Nintendo themselves.

