And the iMac G3 350 doesn't have Firewire, so you can't do a Target Disk Mode from another machine ...
About the only way I can think is to physically remove the hard drive, install it in a USB or Firewire case, and use another iMac which has a DVD to install onto the hard drive, then transplant it back into the machine.
But really, it's doubtful its worth the effort. Apple doesn't officially support OSX on this machine in any case, and the machine is worth relatively little. Reinstalling OS9 may be the best way to go.