samba - Jan 2002 - Authenticating a user in a Windows 2000 domain

I am new to the integration of UNIX and Windows 2000 interoperatability and
I was assigned to a project that will authenticate users in a Windows 2000
environment.  We currently have a script/program that will authenticate
users in Windows NT4 environment (and it is currently working in mixed mode)
but I will need to find a way to do this using a Windows 2000 server that
employs Active Directory (in native mode).

Any help will be greatly appreciated.

Thanks