On the off-chance you haven't heard about it yet, I wrote an article on OpenVPN for Linux Magazine. It's in the April 2006 issue, which has already been mailed to subscribers and should be available at bookstores and on newsstands any day now.
Update (2025-06-08): Hello from 19 years later! The Wayback Machine has an archived copy of the 2006 article: Casting Your Net with OpenVPN.