Mail Backup Retrieval

I back up the contents of my G4 iMac 10.2.8 on to a LaCie hard drive as often as I can remember to.

Retrieving data files and pictures seems easy enough.
But how do I retrieve email messages?
Not a Mailbox - which I can retrieve and see but not open - but the individual Mail messages.

I don't think you can pre-Leopard, when the format changed (short of re-importing the mailbox).

May be wrong though.

Thanks to ian_c for suggesting IMPORT Mailboxes.
Yes that does work OK and once imported into Mail you can read each individual message.
I did have some concerns about confusion between the present and the imported Maibox having the same Mailbox name.
But no worries - the imported Mailboxes are stored in Mail in a Folder called "Import", so it all works fine.

Thanks.

It's always a delight to give accidental good advice!