[Chealion]

Normally when you close the lid, the PB will go to sleep, and on VersionTracker there are a few applications that will stop a laptop from sleeping. I know I've helped answer a similar question. In the same thread (I'll find it and post where it was) it was also mentioned that this isn't the smartest idea because the Powerbooks let heat dissapate through the keyboard also. That could cause problems if the computer can't disappate heat properly.

Found it

iTunes with PB display closed