What's the better user authentication server (Linux Samba, NIS, Win AD, etc)?

Hi,

I'm the system admin for a university, and the actual user server
is Windows 2000 Server + Active Directory. Now, I have clients
Win NT 4 Workstation, Win 2000, Win XP and Linux (Conectiva and
Fedora distributions).

Then, I'd like to change Windows 2000 Server to Linux Server.
What's the better solution for user server?

1st) Linux Samba: I think it's better for Windows clients, but
for Linux clients I didn't see an easy way for these to connect
to Linux Server Samba. I'd like that the user login window would
try to connect directly into server, not locally, and to map the
network user home dir automatically to local /home/<user> dir.

2nd) A hibrid system, with Linux Samba Server for Windows clients
and a NIS/NFS ou LDAP Server for Linux clients. Is this solution
possible? Is it so integrated between client and servers?

3rd) Is there some other solution to solve this? And a solution
with only a single user server, not many server applications?