I've taken a quick look into VPN (as i've not had to set it up on linux before), and it seems that CIPE is probably the best way to go, whether you are using linux machines or windoze. It is built in to fedora, and for windoze, justhead over to
http://cipe-win32.sourceforge.net
On linux you can set up CIPE by heading over to System Settings -> Network
then click on New to add a new network interface, and the first option in the list is CIPE VPN