samba - Nov 2009 - Ask for passwords

Hello Samba!

    I am trying to setup a samba server where windows users (any windows
version) can:

- List all shares in server without ask for password.
- Access 'Public' without ask for password with full access
- Access 'Comercial', this share needs ask for user and password
    
    Any suggestions?

Thanks!

[global]
        workgroup = dotti
        netbios name = Serv-001
        ;netbios aliases = SRV_Contabil SRV_Informatica SRV_Design
        server string         security = share
        encrypt passwords = yes
        unix password sync = no
        log file = /var/log/samba/log.%m
        max log size = 50
        socket options = TCP_NODELAY SO_RCVBUF=16384 SO_SNDBUF=16384
        dns proxy = No
        interfaces = eth0
        bind interfaces only = yes
        #defer sharing violations = no
        guest account = nobody
        #ntlm auth = yes
        unix charset = iso8859-1
        display charset = cp850
        ;include = /etc/samba/smb.%L.conf

[Public]
        browseable = yes
        comment = Servidor de Arquivos
        path = /publico
        read only = No
        public = Yes
        security = share
        guest ok = Yes
        vfs object = recycle:recycle
        recycle:repository = Trash/%U
        recycle:keeptree = Yes
        recycle:touch = Yes
        recycle:versions = No

[Comercial]
        browseable = yes
        comment = Comercial
        path = /comercial
        public = No
        read only = No
        only user = Yes
        writeable = Yes
        security = user
        valid users = comercial