I've searched for a way to control the display brightness from the command line. I found several AppleScripts that open the System Preferences panel and set the slider, but I wanted a pure command line tool. Maybe someone else is looking for the same solution, so here is what I found:
This blog post discusses has a small commandline tool (written by Nicholas Riley) to set the brightness from Terminal. Just download the binary [4KB] and install it. You can then set the brightness by typing brightness 0 (to set it to minimum, use 1 for maximum, or any value between).
Note: The binary is Intel-Only (32-Bit), but the source code is available on the above linked page too, so you could easily compile a PowerPC or 64Bit Intel Binary on your own. I've tested it only with Snow Leopard and a self-compiled 64Bit binary, and it works fine
Mac OS X Hints
http://hints.macworld.com/article.php?story=20090901021817717