OR you could just avoid Dead Pixel Paranoia by going to the Apple Store and before they charge your credit card, INSIST that the EXACT Powerbook that they intend to give you be brought out from the back room and plugged in at the service desk. If you have to, speak to the manager to make this happen. If you make it clear that you intend to purchase that day if nothing is wrong with it, they should be willing to do this.
Use the Display feature and TextEdit to compare the screen in a mostly blue and mostly white background. If there's a dead pixel, you will see it. I definitely saw one when I did this, and I told them to march that piece of trash right back to the back room and bring me another. This avoided the little Apple trick of selling you a PB with a dead pixel and then saying it's not a real mechanical problem. If the pixel goes out in the first thirty days, try bringing it back and get the manager again. If you are super-nice, they might let you exchange it as your "one free exchange in the first thirty days due to mechanical problems"--even though Apple says dead pixels aren't really a mechanical problem, some store managers just want you out of their hair.