If it's the regular DS you're talking about, then matte (or gloss, whatever floats your boat) model paints should do the trick very nicely. Airbrushing is highly recommended, and seek out tips to get an even coating as it will give you results that are second to none.
My brother was into modelling when he was younger, and he built two models of the same car, painted one and airbrushed the other. The results are incomparable, the airbrushed model is simply gorgeous.
Incidentally, I would recommend matte model paint (model being the key word there!) as gloss tends to feel rather uncomfortable under the hands after prolonged use. I know the DS is broken, but for those of you who would like to try it out on one which works...
I also think there are some matte finishes (like lacquer, but not shiny) which will protect the paint form constant contact. I'm not sure about this, but worth a look if you want to preserve your artwork when you're done. Stencils are strongly recommended - they give an amazing effect.
