samba - Mar 2003 - disabling multiple PDC logins from same user

I have a Samba 2.2.7 set up as a PDC, users login into the domain from their
Win2k workstations (user takes a computer that is free and logs on). But
some users are sloppy, and they login into domain from multiple computers at
once. How can I disable this, so that one user can login into a domain only
once? Some kind of locking?

Thanks.