If i understand the question correctly, then you have to swap.
You open the first door, and its a goat, the host then opens a second door, and its another goat. Thats both the goats out of the picture, so if you swap, you are bound to get the car, as there is only one closed door.
You are gaurenteed(sp?) the car if you dont get it first time then swap.
If I am wrong, Peters initial explaination is crap.