New VPN install

We will be opening a remote office in a few months and would like to request some help how would be the best way, but cost effective way of installing. The current main server is running MS Server 2000 and the workstations (three) will be XP Pro. Currently we have a simple domain network with a Linksys router running DHCP. Our ISP has given us a static IP address (cable modem) and our remote office will have the same. Is there a way of doing this without buying new hardware/software?