Cannot access External FW-HD on second mac using Airport network



I have a mac mini on which I have connected an external FireWire-HardDisk. This mini is also connected to a airport netwrk.

When I use another mac which is connected to the same airport network, I cannot find the FW-HD even if I login as a registered user of the mac mini.

Any advice welcome. Thanks
A little extra info after many more tests, the external FW-HD does appear in the "Select volumes to mount" window (after login) only if I login with an admin account of the mac mini.

Ideally I would like to be able to do this using a NON-admin account.
I do have file sharing on as when I connect I get the list of user volumes listed but not the FW-HD volume when I use a none admin account.