Vista - file preview thumbnails in explorer

Hi,
I'm trying to figure out how vista manages the thumbnail previews in
explorer. Specifically video previews. And more specifically how to
extend or overwrite this functionality. For instance, let's say I
develop a new type of video (format or container) how can I develop a
utility that could generate previews. Or let's say instead of
previewing a random frame in a video I'd like to show 2 frames for
wide screen videos depending on the size of the thumbnails chosen for
the folder. These are examples to provide context for this posting,
they are not necessarily exactly what I want to do.

Essentially how do I gain programmatic access to this mechanism?