Loose Change claims
"(1)The buildings simply could not have collapsed from a plane impact or burning fuel: The

melting point of normal steel is far exceeding the burn temperature of aircraft fuel, and this     
steel was not normal. (2)And even if they did melt, resulting in collapse; the building    
could not then have fallen at freefall velocities, as its own resistance would have slowed it       
considerably." 

Scientific American rebuts
"For example, according to www.911research.wtc7.net, steel melts at a temperature of 2,777

degrees Fahrenheit, but jet fuel burns at only 1,517 degrees F. No melted steel, no collapsed
towers. "The planes did not bring those towers down; bombs did," says www.abovetopsecret.com. 
Wrong. In an article in the Journal of the Minerals, Metals, and Materials Society and in    
subsequent interviews, Thomas Eagar, an engineering professor at the Massachusetts Institute of  
Technology, explains why: steel loses 50 percent of its strength at 1,200 degrees F; 90,000 
liters of jet fuel ignited other combustible materials such as rugs, curtains, furniture and 
paper, which continued burning after the jet fuel was exhausted, raising temperatures above     
1,400 degrees F and spreading the inferno throughout each building. Temperature differentials  
of hundreds of degrees across single steel horizontal trusses caused them to sag--straining and       
then breaking the angle clips that held the beams to the vertical columns. Once one truss 
failed,  others followed. When one floor collapsed onto the next floor below, that floor     
subsequently gave way, creating a pancaking effect that triggered each 500,000-ton structure to    
crumble."

Here is a video of molten metal streaming out of the impact area (raw footage, no insinuating commentary) :
http://video.google.com/videoplay?docid=-2991254740145858863&q=cameraplanet+9%2F11