Howdy,
I have 4 computers hooked up to my router, 1 winXP and 3 Linux, and I want to have users logins authenticated on one of the systems. I know that might not make any sense, but I don't know how else to put it. Let me give you an example-
Each user's home directory is stored on a server. When the user logs in to a workstation, his login is authenticated on the server (so that if he changes his password, it changes for every workstation) and his home directory is mounter to /home/username. Each user can only be logged into one workstation at a time.

My questions is - what services does the server need to be running? Do you do this via LDAP or NIS or Samba? I've read some HOWTOs and tutorials on network authentication, but can't seem to figure out exactly what I need to have running. Thanks so much.

With XP Pro you need to authenticate to a PDC or Primary Domain Controller.
This can then pass a profile back to the XP box to add/remove privileges..
Commonly called a Roaming Profile..
With XP Home, it's just a login to the shares, nothing more.

In Linux you can do the same by using the pam structure and the pam_ntlm module.

Samba can be the PDC or preferably Samba-tng