1st off - how far does the machine boot, and does it have a FireWire or IEEE1394 port. The simple answer to your question is first to obtain a Mac OS X boot disc - this could cost rather a lot, and you may find it cheaper just to purchase a iMac G3 with Mac OS X pre-installed. And once you obtain the bootdisc, grab an external FireWire CD/DVD drive and use that to install it
as far as the booting process the machine will turn on with no apple chime sound or video and yes i do have a firewire port
secondly i do have a boot disc but the firmware is not updated so i cant run osx yet