[Samba] Slow copying over samba server to/from Windows XP

[Panics Robert]

Hi!

Just like to know if anyone have the same problem and the solution for this:

At our company we buy that UNKNOWN os called MS XP Pro, after a while the users report some errors when they try to copy to our samba fileserver, before we use Win98 at the client side, and that problem was not observable. 
The copy start at 50mbit/sec and somehow it's stops and just waiting waiting about 10-20 sec, then it go ahead.., it's very pesky.
I was searching at google for the problem, and try several resolution, but they don't work. (Change our HP 4000M switch to another one, Downloaded MS patch, Setting the network card parameters at the registry, trying to set the NIC speed manualy, trying to change the NIC,  modifed the SO_SNDBUF size at samba, and much more.. ) 
Which I see in iptraf, is the copy starts at 50000kbit/sec and after a while it's go under 2000-3000 kbit/sec, then go back to 50000kbit/sec .. and so on.

My HW is a HP Proliant ML330T03 P4 Xeon 2.4G with 512M memory and the same size of swap.. 3* SCSI2 HDD

        netbios name = obelix
        workgroup = WORK
        os level = 64
        preferred master = yes
        domain master = yes
        local master = yes
        security = user
        encrypt passwords = yes
        domain logons = Yes
        logon path =
        logon drive = u:
        logon home = \\%L\%U
        logon script = %U.bat
        add user script = /usr/sbin/useradd -d /dev/null -g 104 -s /bin/false -M %u
        server string = %h server
        wins support = yes
        guest account = nobody
        domain admin group = @ntadmin
        admin users = @ntadmin, root, pampi
        message command = /usr/bin/linpopup "%f" "%m" %s; rm %s
        character set = ISO8859-2
        client code page = 852
        debug level = 8
        syslog = 1
        syslog only = no
        log file = /var/log/samba/%m.log
        max log size = 1000
        timestamp logs = yes
        socket options = TCP_NODELAY SO_SNDBUF=4096 SO_RCVBUF=4096 IPTOS_LOWDELAY
        name resolve order = lmhosts host wins bcast
        time server = yes

+ the shares 

I use this type of smb
obelix:~# smbd -V
Version 2.2.3a-12.3 for Debian
with  obelix:~# uname -a
Linux obelix 2.4.22
type of kernel

Waiting for your answers ;)

Regards, PamPI