[Samba] Question about Samba share security.

[Allen]

Dear All,
 
Sorry about my poor english!
I am using SAMBA 3.0.8 on Fedora Core 3 box.
Otherwise, many winXP_pro_sp2 clients in my subnet.
When I connect to my samba server (use windows nethood.) from one of
clients.
It prompted a window to authorize username and password.
After given my username and password, I will saw my home directory and
public directory very well.
 
But~ the question happened!
When I close the nethood's window with no opening file from samba server,
and waiting more than 5 mins.
I reconnect samba server, it doesn't prompt me the authorization window
again except reboot or relogin.
Why?
What parameter I shoud add in my smb.conf for this security issue?
 
Above is my smb.conf.
****************************************************
[global]
   workgroup = BALI
   server string = Samba Server
   hosts allow = 127. 10.168.22.0/255.255.255.224
   printcap name = /etc/printcap
   load printers = yes
   printing = cups
   cups options = raw
   log file = /var/log/samba/%m.log
   max log size = 1024
   security = user
   encrypt passwords = yes
   smb passwd file = /etc/samba/smbpasswd
   unix password sync = Yes
   passwd program = /usr/bin/passwd %u
   passwd chat = *New*UNIX*password* %n\n *ReType*new*UNIX*password* %n\n
*passwd:*all*authentication*tokens*updated*successfully*
   socket options = TCP_NODELAY SO_RCVBUF=8192 SO_SNDBUF=8192
   interfaces = 10.168.22.1/27
   local master = yes
   os level = 255
   domain master = yes
   preferred master = yes
   wins support = yes
   dns proxy = no
   deadtime = 5
   dos charset = CP950
   unix charset = BIG5
   hide dot files = yes
#============================ Share Definitions
==============================
   idmap uid = 16777216-33554431
   idmap gid = 16777216-33554431
   template shell = /bin/false
   winbind use default domain = no
[homes]
   comment = Home Directories
   browseable = no
   writable = yes
   valid users = %S
   hide dot files = yes
[printers]
   comment = All Printers
   path = /var/spool/samba
   browseable = no
   guest ok = no
   writable = no
   printable = yes
[public]
   path = /home/public
   public = no
   only guest = no
   writable = yes
   printable = no
****************************************************
 
Thank you very much!