When I got my PowerBook, I noticed it got ridiculously hot when using it under normal load. This is because the fans don't turn on until the machine gets really, really hot. A program called G4FanControl can help with that problem.
The GUI version runs under Leopard, but requires you to run it every time you log in, and enter your password. Once you do this, you also have to re-set your temperatures, because the app does not remember them. I found a way to work around this problem -- this earlier hint suggested a fix to this, but didn't give any code. After a couple of hours, I finally figured out how to do this (I had to learn how to make the script).
Things you will need for this:
cd /Users/youruser/path/to/g4fanctrol/command/line/app
./g4fancontrol --set nn
Replace the /Users/youruser... bit with the full path to the command line app, and replace nn in the next line with the desired target temperature in Celsius.Mac OS X Hints
http://hints.macworld.com/article.php?story=20080317181202447