drcube: Well you have to consider that hydrocarbons can only burn at about 1800 degrees fahrenheit in the atmosphere, under perfect conditions (a gas stove, for example). Steel doesn't melt until over 2200 degrees. That means steel doesn't collapse. The towers were built in such a way that it wouldn't be possible for them to collapse because of a few destroyed beams. In fact, it's well known that during heavy storms the towers swayed more than they did after the jet impacts.
Also, mineralGod is right about Tower 7. Larry Silverstein admitted to demolishing it, yet the FEMA report still states that it collapsed due to fire. The fact is, no steel building has EVER collapsed due to fire, in the history of steel buildings. I'll bet you it'll never happen again, either, mostly because it didn't happen on 9/11. The buildings were demolished.
You can watch the footage of tower 7, like mG was saying, and see that the penthouse atop tower 7 collapses inward first. Considering that they hardened a couple of floors about halfway up, tower 7 was even stronger than the other buildings, plus it was across the street. There's no way a couple of small fires could have destroyed the building.
Additionally, there are transcripts available of firefighters communications prior to the towers collapsing, and you can see that they were in no way worried about the buildings collapsing. They nearly had the fires under control in many places, actually.
