In EV admin console, for each mailbox, there is a permission setting to control who can read, write or delete other's archive.
I have two users "alpha" and "beta". I add alpha into beta mailbox as read and write enabled.

Then I use alpha to login into a XP with Outlook 2003, I create outlook profile for alpha which I can retrieve his archive correctly. Then I create another profile for beta, which I still logon as alpha. I still can retrieve alpha's email correctly.

However, when I use alpha profile in Outlook, I add in the beta account using the following procedures: Tools -> Email accounts -> View or change existing email accounts -> Change -> More Settings -> Advanced. I can see both alpha and beta's email at the same outlook screen. However, as I log in as alpha , I cannot retrieve beta's email. I can still retrieve alpha's email.

It just return the shortcut to me when I click it . I found there is no way to open it.