What mode what the server in, as in, was it running as a DC?
Do you have any type of synced directory? eg are Active Directory users available in SME, and vise versa?
If not, this is something one of the linux gurus should make - it would raise the bar on Linux distros so high...
www.padl.com have nss_ldap and nss_pam which can look up users for auth in Active Directory, could this made into a module for SME?