Looks like someone finally wrote a no-sleep extension that really works. Insomnia (GPL) appears to be a rewrite of the old OS 9 Insomnia extension for OS X. Combined with a couple commands shown on their front page, it provides a quick and easy way to prevent your PowerBook from sleeping with the lid closed.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20050308172947974