I migrate samba 3.0.25 to samba 3.4.3 because the old version don't work with seven in a domain samba.
i migrate smbpasswd to dbsam, my [global] smb.conf under :

[global]

# workgroup = NT-Domain-Name or Workgroup-Name
        workgroup = domtest4
        netbios name = SRVTEST4
        server string = Serveur SAMBA TEST REDHAT4
        encrypt passwords = yes
        #smb passwd file = /etc/samba/smbpasswd
        null passwords = Yes
        #passdb backend = smbpasswd
        passdb backend = tdbsam
        name resolve order = wins host lmhosts bcast
        log level = 2
        log file = /var/log/samba/%U.log
        #domain admin group = root
        admin users = admin root
        domain logons = Yes
        security = user
        os level = 95
#        os level = 65
        preferred master = true
        domain master = yes
        dns proxy = No
        wins support = Yes
        #local master = true
        #template homedir = /home/
        logon script = logon.bat
        logon path =
        logon home =
        hide files = logon.bat
        username map = /etc/samba/smbusers
        guest ok = yes

Now i try to create new users with this command :

useradd -c "SMB INFOS" -d /dev/null -g serv_direction -s /bin/false test1
i use pdbedit 
pdbedit -a test1 -h=/home/users/test1
passwd

After on windows xp or seven i try to declare a new user, the answer is user test1 not find in domain domtest4.

i don't now why !

best regards