I've only done this with Outlook 98 - but I imagine it's the same. It should at least point you in the right direction.
You can assign permissions to other users in Exchange Administrator, but keep in mind this will let those users access the entire mailbox (mail, journal, etc.). The alternative is in Outlook.
In the user's Outlook who wants to share, Right-click the Contacts folder, select Properties, then Permissions. Assign permissions, and appropriate rights to the users you want. Then in those users who have been given access, you need to add the shared user's mailbox to their Exchange Server setup (Tools, Services, Microsoft Exchange, Properties, Advanced, Add...)
Then the shared contacts folder should appear in the folder list.