MacBook brightness set to zero suddenly resets itself to one. Any ideas why?
The 2007 MacBook (without "Pro") doesn't even have an ambient light sensor, so that one can be ruled out. My guess would be that some software, maybe even the system itself, turns the background light back on to let you know that the machine is still running.
If you're on Snow Leopard or Lion, you could use the Screen Saver prefs to assign a "Hot Corner" to "Display Sleep" which turns off the display without putting the computer to sleep.