Hmm, varför är det ingen som går och kollar med Apple?
http://docs.info.apple.com/article.html?artnum=88064 ger alla detaljer:
Using your PowerBook G4 with the display closed
You can use a PowerBook G4 and PowerBook (FireWire) computer by closing the display and connecting an external monitor.
1. Close the PowerBook's display. The PowerBook will go to sleep.
2. Connect the AC power adapter and an external monitor.
3. Turn on the external monitor.
4. Connect an external Apple USB keyboard and mouse. The PowerBook will wake from sleep. If you have an Apple display that also has a USB cable, connecting this cable will also wake up the PowerBook.
To use the internal display again, choose Sleep from the Apple menu, then wake the PowerBook by opening its display.
Tips
1. When you use your PowerBook with the display closed, you can't take advantage of Video Mirroring. If you have both a VGA and S-video source connected to the PowerBook, only the VGA device, usually an external display, will have an image.
2. Connecting an external monitor increases the power requirements of the PowerBook. Therefore, you must use the AC adapter whenever the PowerBook is connected to an external monitor. The PowerBook will not wake up if the power adapter is not connected, and if you disconnect the power adapter the computer will go to sleep.