samba - Jul 2002 - http://lists.samba.org/pipermail/samba/2002-July/075880.html

Dina, I was able to get XP to logon to my samba PDC running 7.2. If you 
are still having problems, shoot me an email and I will be happy to 
help. I had all of my trust accounts set up right, NT and 2k systems 
could logon to the domain, but XP could not. Then I remembered, the 
first time you logon to the domain, you must logon as root. Once that is 
done, XP will need to reboot, then you can logon as any domain member.