(this is also currently entered in the game.life challenge, so please vote.)
Step 1: Materials
1 nintendo DS or DS lite (I am using the DS lite)
1 XACTO Knife
1 sheet of sticky photo paper or computer skin paper
1 R4 DS card with a micro SD card http://www.r4dsshop.com/
1 Micro SD card reader
And thats it!