Power the computer down, remove power cable (and other cables that can carry electricity) and let residual charge drain. Open lid and remove the green jumper. Reboot and you're done. Maybe you want to put the green jumper back not to loose them (you can also apparently leave it attached to pin 1 or pin 2, but not connect both pins).
Macs don't have a BIOS. They have something called Open Firmware instead. So the BIOS password is called Open Firmware password. You boot into Open Firmware by pressing the command (=apple), option, O and F keys simultaneously during system boot. To set the password type password To enable the protection type setenv security-mode full An then reboot by typing reset-all Apart from the full security mode you can also set "none" (= don't ask password during boot) and "command" (=gives you only limited access to Open Firmware without the password.
Why do all hardware producers make up their own key combinations to access the BIOS? I never remember. This time it was an old DELL, that forced me to download the user manual: It is Ctrl+Alt+Enter. I needed to change the boot priority in the BIOS to enable scsi booting. Funnily grub confuses the disks and you manually have to specify the correct root(hd0,1) in the /boot/grub/menu.lst. Grub writes its guess of hard disk order to /boot/grub/device.map, but the guess was wrong in my case.