OL2000 cannot look up groups in address book via LDAP

[KT]

My company recently implemented a Notes Domino server and
most of our users are using Outlook 2000 as the email
(POP3) client. When we try to use OL to access the
company address book using LDAP Directory Service, we
cannot look up any groups. However, we can look up
individual user accounts. But when we setup Outlook
Express for LDAP lookups, we are able to search for
groups. We'd like to do the same in OL2000. Anyone has
any ideas why we're seeing this behavior and how can we
fix it?

Thanks.