FC2 authentication with Active Directory

[Klaasjan Brand]

Don't know if this helps, but I've set up windows domain
authentication on a RHEL3 server by using the winbind module of samba.
There's a lot of documentation about that in the samba package.
Shortly, you can configure samba to join a domain and install a pam
module that uses the samba-provided credentials to authenticate system
users.
If anyone needs a detailed description I probably should write a howto ;)