samba - Jul 2004 - samba and windows logons with roaming profiles

I have got smaba 3.0.4 running as a PDC on a mandrake linux server utilizing
roaming profiles  and would like to be able to limit a users login to one
per network.  Does anyone have any examples of a logon/logoff script that
say for example creats a file and checks for it upon logon if its there it
would not permit the user to logon until they loged out of the other
machine?? or is there a damon i can run on my server to keep track of this
or will samba itself do it?? ANY ideas will be much appreciated!! Please
help, Mark