SSO on LAMP Stack with AD 2008

We have been trying to implement single sign-on on our Drupal install using LDAP module (kerberos). We have a LAMP stack and Windows AD (2008). We cannot seem to get this to work. Does anyone have a working install with SSO? We have a connection between Drupal and AD (i.e. we can query AD from the LDAP module). But credentials are not being passed (or accepted) from browser to drupal.