Postcard flip, How do you do this?

programming flash
1

Hi There,
I’ve seen the postcard flip on a few sites, and was wondering how they are doing it. I know I can make about 20 images to create the effect, but that doesn’t seem efficient.
These are the two sites that I saw the postcard flip are:

http://www.matthewmahon.com/Click on the center image the guy with the red cross.

http://www.brokebackmountain.com/ecards/

Thanks!
jan