Active directory alternatives for debian

[binary dreamer <dreamer.binary@gmail.com>]

hi. i am running an Active Directory(AD) in a winxp environment of 30 computers.

i am looking to change the AD to a linux pc. is there an easy to use alternative with GUI (even with webmin).

All we need is to have the computers authenticate to the server by username/password/local_domain. once the user is logged in, then the profile will have the thunderbird,  user's files, user's network drive and a softphone profile (such as zoiper, 3cx, xlite, draytek).