XML galleries and image transitions in AS

Ok I have been wondering for a little while as to how to do this but some websites out there load images using XML. All that is fine, what I dont quite get is how to make the nice transition between photos? The best example I can provide is on my friends website he recently completed: http://www.ameereehal.com

(Go to the portfolio section and browse some pictures)

Can anyone provide any tutorials on how to do this as I could not find much on Kirupa regarding this?