The Mac OS is 9.x. And yes, the other computer logs on by using the "Hosts" button.
Let me see if I can clarify all this. The database is hosted by one Mcc running Mac OS 9.2. The other Mac (OS 9.1) attempts to log on, if the HDD is named anything other than "Cath's HD" the screen says login is not allowed from that computer.
If anyone needs clarification, please ask...
Rob