i believe that if you installed the os 9 drivers when you formatted the disk, then it should be no problem to install from the os 9 installation disk. otherwise you need to reformat and install the os 9 drivers on the drive.
I read a thread about this on another site, I think it was osxfaq.com, where you can start the X install and do a custom just installing the 9 drivers. Don't know for sure if it works.