Damn, I came here eager to try out all this and hopefully be of some help with my newly-acquired PPC Mac Mini 1.5GHz, only to see I missed this key part in bold letters:
Can you guide me a little bit how i can do that?
I have an mini mac at work and could bring another mac laptop if its needed for the remote console output.
Have a second Mac that can boot OS 9.
Start the mini in target disc mode.
Connect to second mac.
Download this http://macos9lives.com/smforum/index.php/topic,2143.0.html and run from the second Mac, but use the mini's disc as the install location.
Remove the installed ROM from the mini and replace with the special one provided here.
Reboot the mini into open firmware.
I don't know if all the right OF commands are in this ROM to enable boot so you might need to change the compatibility property at the root of the device tree and the cpu version in the cpu node of the device tree.
Then just type boot.
The problem I have is, while I do have 2 Macs that can run Mac OS 9, neither of them have FireWire 400 (or even 800): one is a PowerBook Wallstreet G3 266MHz (which lacks even USB), and the other one is an iMac G3 333MHz that only has USB 1.0 connectors.
Aside them and the Mini, my only other Mac is the G5 Quad-Core, so...
I tried checking if there were ways to somehow use Target Disk Mode with just USB, but apparently not. (Only
booting directly from USB seems to be possible, but that's not enough.)
I will see if I can borrow a Firewire and Mac-OS-9-capable Mac from a local shop (or order a PC Card with Firewire for the Wallstreet), but until then, I'm sorry to let you guys (ELN and Nanopico especially) down on this one for now. :/