You will have to boot from an MacOS X install DVD and under the Utility menu is an option to set the firmware password. There are options and remember what you password is as resetting it can be more than a bit of a challenge. I am a Apple Certified Mac Tech and have only had to do this once and depending on the mac, shorting out a couple of pin/pads on the logic board. So write it down and put it somewhere where you will remember!