I've just set up an Open Firmware Password for the first time. My understanding is that this would prevent booting the Mac from another volume (ie an OS X install DVD). After setting up the password and rebooting my machine, I decided to test things out by inserting my OS X install DVD and selecting it from the "Startup Disk" preference pane. Lo and behold, it rebooted from the DVD without asking for the password. Any idea why this happened?