Changes for Windows XP to join the Samba Domain
The following steps have to be done with an local administrator or a member
of the local Administrators group.

This steps must be done before joining the Samba Domain (D-PHYS Domain
Logon):


Changes for Windows XP (all versions)
Start the Administrative Tools (Start / Settings / Control Panel /
Administrative Tools). From there start the Local Security Policy. 
In the Local Security Policy open Local Policies and then Security Options. 
Disable the following entries: 
Domain member: Digitally encrypt or sign secure channel data (Always) 
Domain member: Digitally encrypt secure channel data (when possible) 
Domain member: Digitally sign secure channel data (when possible) 
Domain member: Require strong (Windows 2000 or later) session key 


In the Group Policy Editor (C:\windows\system32\gpedit.msc) enable the
following entry: 
Computer Configuration\Administrative Templates\System\User Profiles\do not
check for user ownership of roaming profiles folders 

Fonte: http://nic.phys.ethz.ch/readme/45