It's really not hard, see the samba documentation.

http://samba.org/samba/docs/man/Samba-HOWTO-Collection/FastStart.html#id2555963

Basically install the kerberos packages for your distribution, run the
domain join command, test getent password <username>, make sure you
know the root password (just in case...) and edit nssswitch.conf and
the pam configuration.

Check the documentation for specifics.

-- 
Andrew S. Zbikowski | http://andy.zibnet.us
IT Outhouse Blog Thing | http://www.itouthouse.com