client windows xp machine-only authentication

Hello I implemented successfully a wireless-access for clients windows xp with authentication of the machine (in a samba domain) and the users (in a samba-domain) to my openldap-DB with freeradius. This works fine. My question : somebody have configured windows xp(SP3) to make only a machine authentication ? I was not able to restrict this. My windows xp-clients makes first a machine-authentication and then allways a user- authentication. It is more a windows-question for a microsoft-mailinglist - i now - but i think a lot of freeradius-users use like me windows-clients and certainly somebody have a solution for me. by luis