These (video, video) are supposed to debunk the conspiracy theories that “that wasn’t flight 77 that hit the Pentagon!” I’m not a particular believer in those theories, but I don’t see how these could prove a whole lot either way. If you look carefully you can see something horizontal and white coming in from the right on one single frame, and then badoom — big explosion. Maybe it’s possible to gauge the size and prove it’s a big passenger jet, I dunno. None of this is anything I could possibly judge as a layman. But if you want to see the videos, there they are.
I think it’s pretty darn well established that those were passenger jets hitting the Twin Towers, so I’m not sure what’s up with the obsession that this wasn’t one. Any conspiracy theory you forge is going to have to take the Twin Tower jets into account, so I’m not sure why proving there wasn’t a third jet involved could be such a big deal.
The CNN coverage of these videos is pretty good too; the little video there features the CNN dude that was there the day it happened, and he points out that something he said that day was taken badly out of context on the “not Flight 77” websites. On the flipside, he does discuss things like other videos supposedly showing the plane still being denied/under wraps.