<div class="quote_poster">Quoting huevonkiller:</div><div class="quote_post">Just read the loosechange guide. Don't waste your time on this video any longer. These people made a ridiculous amount of factual errors.</div>
I read a some of the sections that I thought I would be interested in the guide and although it pointed out some errors, it didn't explain a lot of things.  (And had a lot of mocking remarks)
My biggest question I guess is what caused the two towers to fall? (Especially the way they did at the speed they did)
<div class="quote_poster">Quote:</div><div class="quote_post">To summarize the aircraft:
The maximum takeoff weight for a Boeing 707-320B is 336,000 pounds.
The maximum takeoff weight for a Boeing 767-200ER is 395,000 pounds.
The wingspan of a Boeing 707 is 146 feet.
The wingspan of a Boeing 767 is 156 feet.
The length of a Boeing 707 is 153 feet.
The length of a Boeing 767 is 159 feet.
The Boeing 707 could carry 23,000 gallons of fuel.
The Boeing 767 could carry 23,980 gallons of fuel.
The cruise speed of a Boeing 707 is 607 mph = 890 ft/s,
The cruise speed of a Boeing 767 is 530 mph = 777 ft/s.</div>
http://www.whatreallyhappened.com/boeing_707_767.html
The impact itself would have only affect girders on a few floors in a certain area.  I think the core would have been intact.
There have been steel framed buildings with strong fires for longer periods of time that haven't collapsed.  Sometimes as long as 19 hours.  
<div class="quote_poster">Quote:</div><div class="quote_post">    *  ~1510?C (2750?F) - melting point of typical structural steel
    * ~825?C (1517?F) - maximum temperature of hydrocarbon fires burning in the atmosphere without pressurization or pre-heating (premixed fuel and air - blue flame)
Diffuse flames burn far cooler.
Oxygen-starved diffuse flames are cooler yet.
The fires in the towers were diffuse -- well below 800?C.
Their dark smoke showed they were oxygen-starved -- particularly in the South Tower. </div>
http://911review.com/coverup/fantasy/melting.html
What do you believe is the reason for the collapses? Maybe it was from buckling from the weakening of steel, but I don't know if 50% strength steel wouldn't be strong enough to do its job.  Especially if it were only on a few floors and there are thousands of joints.