7492 » How do I configure unauthenticated access for the Routing and Remote Access Service, or for the Internet Authentication Service? 28-Nov-03
Microsoft Knowledge Base Article 826156 contains the following summary:
This article describes how to configure the Routing and Remote Access service or the Internet Authentication Service (IAS)
to accept unauthenticated access. By default, the Routing and Remote Access service and the IAS service use the Guest account
for unauthenticated access. This article discusses how to enable these services for unauthenticated access without using the Guest account.