For example, let's suppose that you have two Windows 2000 servers, connected to the Internet by DSL access router/firewalls. Your servers don't need to push high-volume, latency-sensitive traffic between them. Your objective for the VPN is simply to stop eavesdropping over the Internet, but you're not terribly worried about robust security.
In this case, you could configure the Windows server at office A to accept incoming VPN connections, choosing PPTP as the type of VPN connection required. Configure the Windows server at office B to initiate outbound PPTP VPN connections to the public-facing IP address of the DSL access router at office A. Configure your access router/firewall with a one-to-one (static NAT) mapping so that incoming PPTP and GRE are forwarded to the WIndows server inside office A's private network. Configure both servers with accounts to be used by this VPN connection for authentication. To learn more about exactly how to set up a PPTP VPN between Windows servers, consult Microsoft's website. Consult your router/firewall manual to learn how to map incoming VPN connections to your office A server.
There are many possible variations on this simple scenario: