I'm up for it, it's a quick task (install openvpn on ubuntu, set up route, generate certificate for users, run server, give cert to users, who drop in their openvpn config folder, and connect, voila!)
it's fine if your linux is behind router, openvpn only needs 1 port open, so you can easily configure your router to redirect just one port to your linux box.
we'll have to configure tap instead of tun here, because of Windows file sharing requirement. PM if you need further info