At the moment it isnt possible to trigger a DC animation with scenes, although i believe it is on the wishlist. So no, you cant (easily) make components change relative to the scene.
There currently isnt a way of inserting a video in to a scene, either, although i believe some of the ruby chaps are working on it. no guarantees, though.
On to what DCs can do: essentially they let you give components parametric behaviours. Basically what this means is you can say to the component "If your x metres from the origin be blue." or "if your x metres high have y steps." Thats a pretty simplistic way of looking at it, but it should hopefully give you the right idea.
You can always check out the 3d warehouse for some examples of DCs and what they can do.
p.s. speed demon gai beats me to it once more.
