great multi-platform vpn solution
I've been using OpenVPN for years now, and it's proven to be a solid and reliable solution, not only for use with Linux, but also with Windows as well.
I commonly setup a Linux based OpenVPN server and deploy Windows clients.
Very easy to use and can be NATted easily, not like with IPSEC.
I can also highly recommend the graphical front end for windows (OpenVPN GUI for Windows) which is also packaged as a complete installer including OpenVPN. It's available from http://openvpn.se/
i went through and looked at a whole pile of wiki projects, and this is by far the best from a user interface and installation viewpoint.
i got it up and running in minutes and it works fantastic. well done!