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And to comment on other people's comments. Zapping the PRAM will not bypass the password. And you would not be able to put the computer into Target Disk Mode. No Single User Mode, No Verbose Mode. The reason none of these work is because one thing the password protects is that it does not allow you to use any kind of keyboard commands to alter the startup of the computer.

If you use Screen Saver password. Set your computer to require login on boot, and use Open Firmware password then someone would have to take your computer apart to bypass your security. Which means if it is stolen, then you are tough out of luck.