For Ubuntu try :
http://www.techlicity.com/linux-server-and-ms-active-directory.html
http://www.ubuntugeek.com/how-to-integrate-windows-active-directory-and-samba-in-ubuntu.html
If you want more easiest solution, then you should try Open Source LDAP for
CentOS:
Thanks for your reply. All of the solutions need a running Active Directory
server which is not the solution. If I already have an Active Directory
server, why would I care for an additional Linux server?
I need a standalone Linux server which can authenticate Windows/Mac clients.
If it is not
