What is an Open Firmware Password?
Open Firmware is located on the computer hardware. It has nothing to do with the hard disk. It retains settings with an internal battery. One of the settings is security, which allows administrators to “lock” which disk the computer will boot to. You can override this at boot time by holding the option key. You will be asked for the Open Firmware password and then you can choose your boot disk. For more information read this Open Firmware document.