All of the juicy details needed to control a camera from your Nintendo DS are now available at the Open Camera Control project. This is the descendant of [Steve Chapman's] setup from a few years ago. The system has been polished up and has seen many feature additions. It’s been used in movie production and works with a wide range of cameras.
Start by building your own interface cable using an AVR microcontroller running the Arduino bootloader. Finish up by loading some open source software onto the DS to add a cornucopia of shot options.