don't know about login as root, it's generally a bad idea to enable root as a login under OSX. If you do have elevated privileges, getting "Permission denied" makes no sense. The typical way to get elevated privileges in OSX is to use "sudo"
Without the exact error messages together with the command, I can only guess.
Using your G4 booted into 9 will most likely not work. The intel OSX disks will be formated GPT and I don't think OS9 will understand GPT disk format.