2000 authentication in 2003 AD

Hi,

I have run in to a problem while testing our app in AD 2003. Our client
management software which runs on Windows 2000 server send authentication
fine to NT4 domain but when you run the same app in Active Directory the
authentication doesn't work. If I run this app on NT4 server in AD the app
works fine as it's using the PDC emulator to do authentication. This app is
not AD aware. My Question is, can I force a Windows 2000 server to only use
the PDC emulator to service authentication requests. If I can't I will have
to bring back my NT4 servers and use them in Active Directory.

Thanks
Alex