Today I had to join a Windows XP to an SME Domain, after searching and searching I couldn't make it join the domain.
Kept saying that the domain was not found, this is right at the end of the wizard.
This is how I managed to make it happen:
After applying the registry keys provided (the ones that change the security settings)on the resources folder, next:
1- Add NETBIOS protocol to the card that will be making the connection.
2- Right-click "My Computer" > Properties > Network ID > Properties > More > Check use DNS sufix and add your domain to it (name and not IP).
3- Reboot the machine
4- Join the Domain as usual