samba - Mar 2005 - Login from XP problem

Hello
 
I have installed my very first linux box today. I'm using samba to put
it into our Windows (AD) Domain.
I've successfully added it do the domain, but when I try to access it
from my I get "incorrect name/password".
 
I'm using heimdal kerberos 5 (downloaded it today from
packages.debian.org, so I guess that it's the latest one).
 
What can be wrong? =)
 
Many thanks,
  Jonas