Not sure why this is difficult but ... I have the mailbox rights permissions set for a domain user to "read permissions" and "full mail box access". In Outlook 2003, I can add that contacts to a particular user's shared contacts no problem then open and make changes to it.
The question is ... how to send email from an entry in that shared contacts address book? It doesn't show up in the "Tools / Option / Address Book / Option" list to add as an address book.