Basic VPN Questions from a Newbie

Here's the story. Our office has about 10 computers hooked up via an ISDN connection through a Cisco 760 series router. All the computers run Windows 2000, but we don't run an internal server - we just have one dedicated Windows 2000 computer which shares files.

So, do we need to install a server to use VPN? Can you link me to any resources that would help me set this up? Am I in over my head? :)