How to do this....so cool

Maybe it’s an old trick but i really like this effect:
www.margecasey.com
How did they do it? A friend of mine said that is done with slidehowpro…is it possible?
It looks too smooth for a program like that, looks like dynamic masking and xml…
Do you guys have any idea or tutorial that i can study to do this really nice effect?
Thansk so much
J