Hello, Somebody from England on this list, wanted help loading OS 9 on his MDD. I no longer have the original message, so if he will contact me, I might be able to help. As I recall he had Tiger on his MDD. Since I also own a MDD, I can verify that the retail edition of OS 9.2.1 cannot be installed without wiping out the OS X on it and vice-versa. It is necessary to have the System Restore CDs or DVDs that were packed with the MDD from the factory. The exception might be, and I haven't tried it, is to partition the hard drive and put OS X and the retail 9.2.1 on separate partitions. Cordially, Bruce Ryan Nakamura