Best way to create a vpn between two windows machines?

openvpn - free & open source. works fine not only under linux but also for windows.

To note the opensource/community edition is free, there is a commercial version too.

If you're using Windows machines, client OSs can accept up to 10 incoming PPTP VPN connections (EDIT: only in the Professional or Business editions of Windows accept up to 10 connections; Home editions only accept 1 incoming connection) as per these instructions. Of course, Windows has built-in PPTP VPN client capabilities so there is no software needed. You'll need to edit the router that the receiving computer is behind to forward PPTP ports to the newly created VPN "server". The real question is: does the router that the receiving computer is behind pass GRE through?

Hamachi (http://hamachi.cc/download) provides a very easy setup for a VPN, after setting up your server, you'll just need to configure your router to open up the applicable ports.

Check out http://www.itsatechworld.com/2006/01/17/hamachi-vpn-solution/ for a quick setup guide.