I Can't Join a Windows 2003 PDC
Windows 2003 requires SMB signing. Client-side SMB signing has been implemented in Samba-3.0.
client use spnego = yes when communicating
with a Windows 2003 server. This will not interfere with other Windows clients that do not
support the more advanced security features of Windows 2003 because the client will simply
negotiate a protocol tha both it and the server suppport. This is a well-known fall-back facility
that is built into the SMB/CIFS protocols.