SAMBA Domain Controller

Samba Domain on XP:

Start->run->MMC
->File->add/remove snap-in->Add
-->Add
--->Group Policy Object Editor->Add
---->(Group Policy Object must be 'Local Computer')->Finish
--->Close
-->OK
->Local Computer Policy
->Computer Configuration
->Windows Settings
->Security Settings
->Local Policies
->Security Options
->Disable "Domain Member: Digitally encrypt or sign secure channel data (always)"
Restart, and you should be able to log on with your Samba username and password.

For Windows7 and Server 2008R2, also edit the registry:

HKLM\System\CCS\Services\Netlogon\Parameters
add DWORD  RequireSignOrSeal = 0
add DWORD  RequireStrongKey = 0

Reboot after this

Optional

HKLM\System\CCS\Services\Netlogon\Parameters
add DWORD  RequireSignOrSeal = 0
add DWORD  RequireStrongKey = 0

Also reboot after change