Accessing NT security info

Anjuna Moon

I'm not quite sure how to phrase my question, so I'll put it like this:

I'm working on a multi-client application for which I originally intended to make an administrators version of, that handled user-rights and roles. However, my client wants to use NT security for this, so all they need to do is add some NT-roles to their network-clients that decide their rights within my system.
So, my problem is I don't know where to start looking for information on how to do this, which classes in .Net that might provide a way to find the roles the currently logged in user has.
The whole network including the domain-controller use Win2000.

Hoping urgently for pointers.
/Chris