samba domain as realm

hello is it possible to use samba(+ldap) domain name as realm ? i want that if on a XP laptop plug on my NAS (switch) DOMAIN1\username log on , the ldap+radius is authentificate on DOMAIN1 ldap server DOMAIN2\username log on , the ldap+radius is authentificate on DOMAIN2 ldap server the username can be identical but the ldap domain differente my problem is that if the username exists in the DOMAIN1 ldap server, DOMAIN2\username will never get his good VLAN-id (from users file), freeradius give him DOMAIN1\username vlan-id... i 've try ntdomain realm but it doesn't work any tutorial ? thanks