The best way of getting a DOS running on the DS would be to port DOSBox, but the chances of this actually running anything are extremely slim. If you want DOS on the move you should check out the GP2X. The processors in it are almost 4 times more powerful than the ones available in the DS and it also has 16 times the amount of ram. It can run quite a few DOS games within DOSBox, but the speed still isn't brilliant.
You should have a look at porting CloneKeen to the DS for getting Commander Keen running.it whould by cool if the whole comander keen colection is playable on ds











