I'm quite sure the US has been involved in its share of cover-ups and conspiracies, but to suggest 9/11 was an inside job is quite a stretch. I've read what's available on the Interwebs and it does't wash in my opinion.
For the US to pull off 9/11 there would have to have been 100s and I do mean 100s of people involved. Both towers were hit by Boeing 767-200s traveling at high rates of speed and full of highly flammable avgas. That stuff burns mighty hot. And once it has burned off, which it will do, the fire will continue. Both towers were full of highly combustable materials.
The skeletal structures of both towers were heavily damaged by wide-bodied commercial aircraft before the fire(s) began to take hold. Taking this into account, I am not the least bit surprised both towers fell. Do remember that the maximum take-off weight of a Boeing 767-200 is roughly 395,000 pounds (179,000 kg). Also remember that the -200 has an additional center fuel tank to increase the MTOW of the aircraft.
Belief in an inside job does not equate to proof. No matter how much gobbledy goop one finds on Al Gore's Internet. Now, if you want to talk to me about conspiracies, then lets talk about Roswell.