Newsforge has a very interesting article up covering how to setup NFS for sharing over the internet via VPN tunnels.

"Although easy to configure, it is typically used only to transfer data over an intranet or LAN because of its transparency and security potholes when exposed to the risks of the Internet. However, it still can be employed -- without compromising security -- to share files over the Internet by configuring it to run on a Virtual Private Network (VPN) connection."