Domain controller in Linux?

Greetings.

I have worked with *nix for several years now, but we have never had a domain controller of any kind. With all the talk of Novell and Active Directory, it only makes sence that there is a Domain Controller for Linux that could control both the *nix and windows boxes? (98/2k/xp)

What do you use?
How do you like it?
Links?

Thanks!