yaboot is a bootloader that is used at boot time to pick an operating system to load. Macs that can dual boot allow you to pick the OS to boot from a control pannel. Even if you did install it it's not going to help you boot OS 9, because your Mac is missing the Mac OS ROM chip that OS 9 looks for at boot (thats what apple removed when they dropped OS 9 Support). Unfourtunetly thier is not a lot you can do about that.
I break stuff.