Radius + SAMBA PDC + LDAP

Hi, I'm using samba as pdc and ldap as user database. That all works fine. Now I want to use the ldap database for user auth. for radius. But when I'm looking here http://deployingradius.com/documents/configuration/active_directory.html and some other sources, I read everywhere the same. "Konfiguration of Kerberos" but why? I think it should also with ntlm only? And does this paper is the correct for me? Caus if I understand it correctly in that scenario they are using a MS AD? Thanks Andreas