restore os x boot loader

Hello, I installed Linux and Yaboot and now I want my Mac to boot the way it used to, what do I need to do to restore the OS X boot loader? (iMac G5)

You may need the original install disc/s that came with your Mac. I'm thinking that you might start up from the disc and go to Disc Utility and reformat your HD as a single partition. You would lose all your data though. Wait till someone else has a say about this as I don't have direct experience with what you are asking.