http://rajeev.name/2007/11/08/integrating-linux-into-open-directory/

http://en.wikipedia.org/wiki/Apple_Open_Directory

Looks like a good tutorial at:
http://www.kremalicious.com/2008/06/ubuntu-as-mac-file-server-and-time-machine-volume/

http://linux.sys-con.com/node/803618

Little bit of a hint with mac network logins:
http://hints.macworld.com/article.php?story=20060404091349425

Windows / Linux / Mac integration
http://weblog.bignerdranch.com/?p=6&page=3