Honestly I wonder if something is borked with your disk controller. Can you swap disks at all? (IE, does soft eject EVER work?) Again, correct me if I'm wrong here, but on a Mac you should be able to drag the SYSTEM DISK to trash to eject it and put in a program disk; doing so creates a sort of "phantom" alias to the ejected system disk to basically remind you that the system will ask for it back later. If this wasn't possible a single drive Mac would essentially be useless.