NetWare 6 uses eDirectory that has its own LDAP componet.
Just by adding a few extra fields to a users's profile using "Console-1" (ie UID GID, home directory, shell etc) you can use this for authentication.
It Works quite well - if you can run some form of caching (eg nscd) or a more primitive way - eg a startup script that temporary adds those users to the /etc/passwd file.(else the server takes a hammering!!)
We use it on our network and I must admit it works WELL!
I havent tried it with AD but will be doing some tests soon on it.
For Mandrake 9.1 I've created a GUI tool that eases the setup of the clients.
This will be released soon (under GPL).