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

However, when I use beta profile in Outlook, I add in the alpha 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 beta, I cannot retrieve alpha's email.

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