The question mark is a sign of not having a 'blessed' system folder.
I'd boot from the system disk, run disk first aid, at least, and try again.
If you have any higher grade disk repair software (tech tool, norton, disk warrior), I'd give them a shot first.
Following that, if the G3 has never had OSX on it, I'd check re: firmware updates, minimum version of OS9 needed, etc.
Good luck.
And if all else fails, get Jobs over to sprinkle holy water on your hard drive ;)