How is this effect being done?

The top flash bar on this page -> http://www.themodernnyc.com/modern/modern.html

I am guessing they have three movie clip containers which are loading a bunch of images from an xml. But how are they fading one in and at the same time fading one out in the same container, or is it that they have two loaders on top of each other for all the three frames? Also, have they predefined the transition style and order using tweens in the timeline with fixed images inside flash only, because its not the same for every transition and I don’t know how that can be done using actionscript if one was to load images at runtime.

Any help please?