I have tried to restore my PowerBook 12" from the Restore-dvd that came with my PowerBook when i bought it. When I restart the computer and boot from the DVD the following message appears: "You need to restart the computer. Hold down the power button for several seconds or press the Restart button". So my only option is to restart, and after a few seconds, the message appears again.
Apart from this problem, my PowerBook works fine. I just wanted a fresh install, since I have installed a lot of different apps, that have made it quit slow.