Microsoft Knowledge Base Article 302566 contains the following summary:
This article describes how to configure the security to control who has access to specific newsgroups and who can operate Microsoft Network News Transfer Protocol (NNTP) Service. You can also restrict access on the basis of the client computer Internet Protocol (IP) address. If users connect to Microsoft NNTP Service over a public network, you can encrypt that connection by using the Secure Sockets Layer (SSL) protocol so that others cannot intercept the articles that are sent and received.
NOTE: The security is based on Windows 2000 Server accounts and folder permissions. The access that users have to newsgroups is restricted on the basis of user name and password.