To change the brightness of your screen, hit F14 or F15. This may not work on all hardware, it does work on a cube w. flatpanel display and X 10.1
(cubist)
[Editor: This had no effect on my third-party monitor ... which is not surprising. If it had worked, I would have been truly amazed!]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20011003031855760