The Port 25 blog entry…
…points to a new Microsoft technical document titled: Linux VPN Technical Analysis and HOWTO.
As its title implies, this 33 page PDF document gives both a technical reading of Linux VPN as well as specific how-to information. The work is based on testing using Red Hat and Fedora Core Linux distros.
If you are looking for some Windows VPN help, you might want to check out the OpenVPN GUI for Windows I mentioned in an item in my personal blog recently.