This isn't really too hard to do. If you want single sign on you will need a mix of kerberos and ldap. Extend the Active Directory with "MS Services for Unix", this will add the needed entries for unix password/group. First of all I usually run authconfig to configure PAM, this is a little harded to do manually. Next you need to configure the nss mappings, binddn, bindpw, uri in /etc/ldap.conf. You need to install the CA certificate into /etc/pki/tls/certs/ca-bundle.crt, I just paste it at the bottom. You need to configure your /etc/krb5.conf according to your AD settings. Useful tools for debugging, getent, kinit, "nscd -i". I'm not quite sure if this is all but you have inspired me to write a howto on this.. Good luck!