Using Kerberos exclusively on Windows 2003 server - No fallback on NTLM

[Engr]

I am trying to find out if there is a way to stop Windows 2003 server from
using NTLM to authenticate a user if Kerberos isn't available or didn't
work. In other words, we want to use only Kerberos, but I read somewhere
that if Kerberos doesn't work Windows 2003 will try NTLM. Is that true? If
yes, then how can we configure it so that it doesn't use NTLM or any other
auth mechanisms?

Thanks.

Engr