Right. If the CD doesn't show up at all when holding Option, then that is likely that the drive is not considered a bootable device *or* none of your OS 9 discs are bootable on that machine. There were a couple of different flavors of OS 9 that were machine dependent, or only worked on a certain number of machines. I have an eMac 9.2.2 disc that will only work on machines built before mid-2002 or so.

If an OS X disc won't even boot, then I would definately lean towards it being the drive. Were any of the drives you tried the one that came with that machine?