Random background in flash with Action Script

Hey, I saw this tutrial on Kirupa

http://www.kirupa.com/developer/mx/loadingrandombackground.htm

But what I want to do is pull in a random background png from a folder, and not embed each image in the actual flash movie. Obviously, I would rather load one image, than all 5 in a movie. Has anyone seen any AS code to do that? Thanks in advance.