You really should read the Read Me included in the download, or better yet, see the Related Link near the bottom of this page. These instructions involve modifying your system's BootX file. This file is essential to Mac OS X's startup process, and if the file is absent or damaged your computer will not start up to Mac OS X. Please have your computer's Mac OS 9 CD available in the event that your modifications to this file result in an unbootable system.
You can boot to Mac OS 9 and replace the damaged BootX file with a working backup. The instructions are based on my own personal observations of how Mac OS X 10.2 works on my PowerBook, and could differ from the way it works on your system, or with later versions of Mac OS X. These instructions are provided as-is and any modifications you make to your system are done at your own risk. I assume no responsibility for problems that may arise as a result of following these directions, or an inability to follow them. There is no warranty.