To whom it may concern.
You have to just keep playing the game and doing races and as you procede through it you will earn more characters and karts.
I hope this was useful.
From a mystery person.
so your'e asking how to unlock the fastest kart on mario kart ds. its the hurricane! you will need to... get a gold cup in every 100cc cup but only nitro cups that are: mushroom flower star and...