The OS 9 Disc that came with your mini is unsuitable for use on your Mini as it is designed to be used within the OS X Classic environment. One thing you could try is cloning your iBooks 9.2.2 drive to the iMac (use an USB enclosure for both, and something like Carbon Copy Cloner) to do this. Just out of interest, why dont you put OS X on the iMac (Mine has 10.3 and 10.4 on it and both work fine).