network within a network

I would like to form a small network within (maybe outside?) our existing NT domain-based Ethernet LAN but not sure where to begin. We intend to get a server box (Win2000 server)which holds data for only 3 of our 30 users. It’ll be in the same location with the existing LAN but it will not join the NT domain. What kind of setup will I need in order to allow the 3 users to have access to the ‘stand-alone’ server and the LAN at the same time? Thanks for all help.