Open Firmware Password 1.0.2
The Open Firmware Password application allows you to enable security features in Open Firmware. You can use it to prevent others from starting your computer using a CD or other disk with an operating system on it. You can use Firmware password protection to enhance access security to your computer.
When you set a Firmware password, it prevents others from starting up the computer from a volume other than the one you have chosen as the startup disk (chosen in the Startup Disk preference panel within the System Preferences.) Once security is enabled, you cannot startup from other devices such as an external FireWire disk, a CD-ROM drive, or another partition or disk inside the computer.
For Mac OS X 10.1 to 10.3.9, Download and Install the Open Firmware Password application from this page.
For Mac OS X 10.4 or later, you must use the updated version that can be copied from the software installation disc (located at /Applications/Utilities/ on the disc).
For addition information see the KnowledgeBase article.