As with most useful ideas there are difficulties in implementation that must be overcome first. For starters, the ISP you use needs to accommodate you by setting things up, which may or may not be a problem depending on the ISP. Someone who travels nationally may find a wide range of experiences when it comes to ease of use to various ISPs. Probably the biggest headache will be at the home base where the VPN will need to be administered, not unlike the usual experience we all have where management thinks that this is a good idea, but the resources will not be provided. The current staff will just add it on in spite of the fact it does require expertise and time to install and maintain.
This book goes through the steps necessary to get a VPN up and running with examples that come from having actually done it. It is intended to be a practical book, which may explain why it is a short book, and perhaps why it is an NT-centric book. There a couple chapters on what a VPN is, why you want one and a cost model (something technofolks often ignore).
Three products are explained: Point-to-Point Tunneling Protocol (PPTP), AltaVista Tunnel and the Cisco PIX Firewall, although these are not the only products in the marketplace. PPTP is an obvious choice because it is available with NT. There are a total of ten chapters with lots of diagrams including one on managing and maintaining a VPN.
I think the price is a little higher than it should be and I am still looking for a comprehensive book on VPN, but if you want a light introduction to VPN this is a helpful book. It is a quick read, especially if you know something about networks and security. There is more information available on the net including an IETF draft and some good articles from the press and vendors pages like Cisco.