ElDiabloConCaca said:You can do it by installing NoSleep:
http://versiontracker.com/dyn/moreinfo/macosx/20087
However, I will offer a warning: Macintosh portables, like the iBook and PowerBook aren't designed to run with the lid closed, except in sleep mode. Running the 'book with the lid closed can cause physical damage to the computer which is not covered under warranty.