I've heard all those theories. Don't buy it.
It has all the same problems that most conspiracy theories have... mainly that you take a fairly simple premise (that there are people in the world that don't like the US, and a dozen of them hijacked some planes and attacked us with them, and in our arrogance we missed the clues that would have allowed us to prevent it) and replaces it with a far, FAR more complicated one that involves American government and military hatching an amazingly intricate plan and thousands of people (including the entire press) keeping silent all this time and being involved in elaborate cover-up.
But mainly: I refuse to believe the Bush administration (which proved itself almost totally incompetent in every other regard for 8 years) was at all capable of pulling off such a plan.
Native XWA.Netter (Nutter?)