logged on user list

[Kurthermal]

Hello,
I'm writting an application running on a Samba PDC that has to give 
rights depending on the user who's logged on a client of the NT domain.
I've noticed that in some cases, 'net status sessions' returns several 
sessions of different users on a same windows client (for ex. a client 
machine that has wildly been rebooted). I've also noticed that at logon, 
a XP box connects, disconnects, (...), connects this prevent me from 
getting username at any time.

How can I get this information in a sure way ?
Is there a RPC that can help me ?
Other idea ?


Thanks.