samba - Jan 2005 - Timeout password and UNIX password file

Hi there !!!
 
2 very simple questions for you, specialists :
 
I'm Using Samba on a UNIX 11.i box.
This box has some users defined on it in /etc/passwd, and associated with
/home/<user> home directories.
 
The goal of SAMBA here is for me just to be able for each user to see its own
user directory.
Everytihing working fine so far, except 2 thigs :
 

*	When doing a search computer on my windows 2000, and clicking on it, it is
asking for the username and password to connect via SAMba and browse the user
home dir. But Next time I want to do it again, logging in as a different user
name, the system is even not asking for the user and password again, but just
connecting with my first username and password automatically ... Rebooting the
PC seems to reset it. Is there any kind of timeout I can set so the the system
is prompting me each time for user and password ?
*	I have some users defined on the UNIX box ... how do I synchroniza the SAMBA
password with the UNIX one defined in /etc/passwd ?

Many Thanks !
Cedric.