Harry Potter and the Prisoner of Azkaban

I read at Soundtrack.net that John Williams (who's scored all the HP movies) did an original song that is used in a trailer for the movie... But i'm not sure if it's the same one you're after. Some of the music might be from the Prisoner of Azkaban soundtrack. (link goes to available audio samples)
I already know the song. It was on the second album. (Chamber of Secrets) Song number 19. But thanx anyway! :D
I am wondering what the song in this trailer is called. Here is the link, and it is International Trailer B.
nice trailer well i live in colorado i didn't see that trailer anyways i kinda want to know it to :D