I had the same problem so here is what I did.
Get a USB stick. I used an 8gb but it is way bigger than what you need. 512mb should be enough.
Format it for HFS, and install the os 9 drivers.
Insert your OS9 cd. Open the installer with classic. Install on the USB stick. Then install the update on the usb stick. I had to run the updates a couple of times. They seemed to get an error, mostly about accesing a file. I found that making sure all my programs, including OSX native ones had to be closed.
I made my stick this way starting with 9.04 all the way to 9.2.2.
When booting hold down option. It should find the stick in the boot options menu.
I have booted from the USB stick with one caveat. It enters OS9 but my video mode is messed up and the screen is scrambled. It looks like a video settings error, I can see the desktop and it looks like it booted fine.
For the record I have a G4 800 17 inch screen. I know it can boot OS9 because it booted a rescue cd with os 9 on it.