[Dovecot] Outlook 2007 w/SPA, Active Directory (was NTLM failures with an interesting twist)

Has anyone successfully configured the above to enable Single Sign-On? I would love to move away from Exchange but SSO is a corporate requirement.

Outlook Express works fine with it, but not OL2007, and the latteris the only client I can realistically use.

Cheers, Gavin.