Going from peer-to-peer to Server….

I would like some advice on upgrading frm a p2p network to a server based network. I currently have 12 users setup as a p2p. We have one(1) application that needs to access by atleast three to four users simultaneously. print services are needed all the time. The network will expand to at least 25 all needing access to this application. i need to know how to setup a server into this environment. MY scenerio is this; Use one application, file/print server with an Win2000 OS Server software. If anyone can help with beginnings of a setup it would be appreciated.