samba - Mar 2006 - connecting to samba from 2003 sbs domain client running xp profi

Hi everybody,
 
I have a network which consists of a linux data server, running Samba, a
windows 2003 sbs, and a few xp professional clients which login to the
domain server (2003 sbs).
On the linux box, samba is running, this pc is always on. When i start
the client pc (xp profi) and login to the domain, i can access the samba
shares at full speed. 
Now the problem: When the xp profi client is left alone, for about 15 to
30 mins, something happens to the network. When i then try to access the
shares, browsing is slow as H**L.
Sometimes coming with screens like : enter user/passwd.
The only remedy is to logout the user on the xp terminal, log back in,
and everything is fine again. I have samba running in the most simple
sharing system.
This is the samba config file.. : 
 
 
DATASVR ~ # cat /etc/samba/smb.conf
[global]
        netbios name = DATASVR
        server string = DATASVR
        socket options = TCP_NODELAY SO_RCVBUF=16384 SO_SNDBUF=16384
        workgroup = GOVALOKAAL
        socket address = 10.0.0.200
        max log size = 1000
        log file = /var/log/samba/log.%m
        security = share
        guest ok = yes
        guest account = samba
        encrypt passwords = true
 
[stuff]
        comment = All stuff
        path = /raid/stuff
        writable = yes
        browsable = yes
        read only = no
        guest ok = yes
        public = yes

 
I once, tried to let the sbs figure out who could access the linux box,
but that didnt seem handy to me. To do this i had to add the linux box
to the sbs domain. The account for the linux box on the sbs is currently
disabled. Ive also tested it with this account enabled and this didnt
seem to make much of a difference.
 
Does anyone have any idea on where to start looking, or what to do ?
 
Best regards,
 
Martijn