http://video.google.com/videoplay?docid=7304846209709908270&hl=en
For those of you who didn't watch the video, they state that 4-ton girders ended up 600 ft. from the base of the WTC. There's a lot of hoo-hah, but the guts is a calculation that shows how fast they'd have to have flown as a function of height in order to reach that distance, assuming that the girder flew horizontally. The calculations show that if they flew from the top of the building, they would have to move 50 mph or so, and if they came from the bottom of the building they would have to have flown 250 mph or so. The narrator then blithely points out that air being pushed out of the building as it collapsed could not have provided the necessary force to accelerate the girders to those speeds (noting that if the building was falling more slowly when it started (near the top) than at the end (near the bottom)). Thus, he concludes, it must be the work of explosives.
He then goes on to distract you with a philosophical discussion of facts and theories and crying out for the truth etc.
What he doesn't consider:
1) the possibility that the girders were not launched horizontally, the least efficient possible direction that isn't actually downward.
2) the possibility that the girders might have been pushed out not by the air escaping but by the compressive force of the building above it snapping the girders. Like when you break a stick and the pieces fly away, you don't blame the wind, you blame the snaping of the stick.
3) any computation involving the energy that actually went into the girders as the building collapsed.
4) the possibility that the girders were displaced not during the collapse but during the initial impact of the rather large airplane or the subsequent explosion.
5) the fact that girders bounce.
See, this is the problem with oversimplifying the scenario. The video basically encapsulates a high-school physics approach to the question. This is why teams of scientists, not conspiracy theorists, are hired to investigate stuff like this, and why they take three years and a thousand interviews and a million pages of research. There's a data asymmetry here that conspiracy theorists will always use to their advantage.