LogMeIn's Hamachi is "a VPN service that easily sets up in 10 minutes, and enables secure remote access to your business network, anywhere there's an Internet connection." This is the easiest way to create a VPN network between computers and networks. If you have tried setting up PPTP or on Linux, you'd know what I mean when I say "easy".
Hamachi is popular with Windows users because of its easy GUI interface. Although it supports Mac OS X and Linux as well but both do not have (yet) the full GUI Windows users enjoy. If you wish to use Hamachi on Linux, here's a HowToForge article on how to install it on Fedora.
To me, even if they say it is 10-minute easy, I'd rather setup a VPN service that is standards compliant.
[image from LogMeIn's site]