I do not think tahts flash, its done in Photoshop / Image Ready. You have to do this:
- Make a background
- make a new layer add somthing
- duplicated the last layer then add somthing
- Duplicate the last layer add somthing to it
then continue, when you have enough to goto file you should see somthing like open up image ready or somthing. then in image ready you have to do some stuff. hard to explain search for it on the net