Draw three cards, then put two cards from your hand on top of your library in any order.
"I see more than others do because I know where to look." —Saprazzan vizier
Official Rulings for Brainstorm
10/4/2004 : This is all one effect. You draw 3 and return 2 cards all in one resolution. Nothing may happen between the two. If something triggers on drawing cards, it will go on the stack after Brainstorm finishes resolving.