Here’s a collection of links on VPN, and VPN tunneling. Not authoritative, and not meant to endorse any one approach over another or even how to use the technology.
- Networking 101: Understanding Tunneling (obvious)
- Ensuring Network Security with a VPN (Virtual Private Network) – For Dummies
- VPN Tunnels Tutorial – Types of VPNS, Protocol & More (via About.com)
- What A VPN Tunnel Is & How To Set One Up (seems more oriented towards PCs than servers)
- How to Tunnel Web Traffic with SSH Secure Shell (oriented towards Linux servers)
- How to Set Up a Secure Web Tunnel | PCWorld (similar to #5)
- How to setup VPN server (PPTP on CentOS, RedHat and Ubuntu)? – Knowledgebase – PhotonVPS (if you want to set up a server)