Outlook – Public Contacts

Outlook 2000/Exchange 2000/Windows 2000; I created a public folder for company-wide contacts. When one of my users try to compose an e-mail, they could not see the Public Contacts folder. They click on the To: button, but
the folder is not there. When I tried to add them to the permissions tab in Properties, it tells me “One or more users could not be added to the folder access list. One or more users are already specified.” I have the Default User and Anonymous User listed as Editor. The only other
person listed is me. How do I open this up so my users can see this list when typing an e-mail? They can otherwise see the folder and actually make changes to it, just not when sending e-mail. Thanks!!