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How. Just...how. And, uh, wow. Wow, too.
well, you have to place "markers" on your footage within Blender, and then track their movements through the shot. then, with some data from the source-camera (lens size and whatnot) the tracker can then re-construct the camera movement in the 3D viewport :) it's pretty much the same for objects, though this time the markers move instead of the camera. there's some good vids about it over on BlenderCookie.com, Sebastian König goes over the process of tracking a shot and whatnot. I've tried it, and it's awesome :D