To quickly add a Windows client PC to a Samba Domain Controller do the following:
Firstly on the server side, in a terminal session enter the following
/usr/sbin/useradd -g machines -d /var/lib/nobody \ -c "machine nickname" \ -s /bin/false machine_name$
passwd -l machine_name$
The "machine nickname" is the same name that you called the PC in Windows system properties. The machine_name$ is the name of the PC with a dollar sign at the end - this is needed for samba to account for it as a machine name - not a username.
Once the above command have been entered to create the unix account, then add the following command:
smbpasswd -a -m machine_name
Then join the domain immediately from within Windows system properties, using the join network wizard.