Booting From MAC OS CD? (It won't)

Question

Okay, so someone I knew was gonna throw out an iMac. I hate seeing computers go to waste, so I just took it. They didn't have any CDs or anything with it.
I turn it on, and obviously can't login. I dunno the password and neither do they. I found that I'd need an MAC OS startup disk. So I downloaded one, ad, from near as I can tell, your suppose to hold down "C" during the startup to load from the CD.
Except it doesn't. It just loads the "MAC OS 9.1" screen and brings me to the same login page. I've used multiple disks 9.0, 9.2.1 (I can't fins a OS 9.1 per se). ****, I even through a Windows disk for kicks and giggles.
Any ideas?
(Note: I hear the CD spinning and they are warm when I eject them, so I don't think it's a hardware issue)

Answer 1

While the iMac G3 series can boot OS X, the computer did require
a Firmware Update to be installed prior to booting in OS X. And in
order to install the Firmware Update (a download from Support)
the computer needs to have a running OS 9.1 or 9.2 system in it.
Once a suitable OS 9.1 or later 9 is definitely running the computer,
you can look in the System Profiler to see what the bootROM or
Firmware version is; along with a few other details about the iMac.
It may have already been updated to the proper Firmware version.
Some of the early iMac G3s shipped with OS 8.6; so their original
software packet would be very machine specific and not be able
to support dual-booting to an OS X system and would not be able
to be used to upgrade the essential Firmware Update needed for X.
The computer has information printed on the case, in back or on
the bottom; probably near the ports. This should specify what the
original as-shipped configuration was: processor, RAM, etc. And
you could get a free database download from http://mactracker.ca
to further investigate those specifications to more closely guess
at what model & build-date you have. There are different versions.
In order to run OS X (even boot the X disc in the older Mac) the
Firmware Update should be applied first while it is running OS 9.1
or the proper OS9 version if later - it shipped with. To not install the
later Firmware update, if needed, may cause damage to the iMac.
See this page for the noted applicable early firmware update(s.)
"Mac OS X - Available Firmware Updates"
http://support.apple.com/kb/HT1395
Either firmware 2.1 - or 4.1.9. The oldest iMac takes the lower number
and the higher number applies to later iMac G3 a slot-load optical
drive. First iMac G3s with CRT display had a tray-load optical drive.
So, without looking for a serial number or configuration data on the
case, you can tell if the computer has a slot drive or tray drive. An
early indentifier to start with. And MacTracker is very helpful to have.
{The iMac G3 with FireWire ports could also be started in Target Disk
Mode and checked over somewhat by another Macintosh, via a dual
end 6-connection FireWire cable; or startup attempted by an external
enclosed hard disk drive with OS 9.2, (app folder & OS intact.) Been
long enough ago, I don't recall now if the external enclosure needs to
be a FireWire enclosure for the hard disk drive, but that would work.
The older USB was a bit slow in data transfer speeds, so FW is likely.}
Good luck & happy computing!
{ edited to add words }