How do you unlock Darth Vader in stars wars the triolgy?

If you mean the second game you have to get all the minikits on one of the levels, I can't remember which though.

And If you mean the first game then you have to beat the game completely 100%. Then you should be able to unlock the secret level with Darth Vader and a Stormtrooper.

(This is all refering to LEGO Star Wars)