You run it from a slot 2 flashcart, with a commercial game pak in slot 1. If your DS isn't flashed you'll need to use a slot 1 flashcart or a NoPass (Passcard, Superkey, etc.) to boot the slot 2 cart in DS mode, then you swap it out for the game pak.
Don't forget to apply the DLDI patch if your slot 2 cart doesn't do it automatically.