I ran the 10.4.4 update, and my fans then went flat out. Sounded like 1800nm of thrust out the rear of my machine. Several reboots did not fix the problem. So, irst I played with pmset, and as advised in another hint here, the processor performance settings (set to highest) in the Options section of the Energy Saver System Preferences panel.
Still nothing. Another hint suggested that you zap the pram. So, I did the Command-Alt-P-R, and waited through three "Booooong!" noises. Still my fans went nuts. Then I booted a 'Linux Live' CD, and the fans were normal. Back to OS X, and it was fans-flat-out again. Okay, I then:
Mac OS X Hints
http://hints.macworld.com/article.php?story=20060112090527425