MVVM or MVC? Want to use the same set of classes for WPF and ASP.NET

Question

I am a newbie in terms of Design Patterns. I just started learning MVC when I am hearing a new buzz, MVVM.

I want to learn the insights of both of these by redesigning an old inventory and invoicing application I developed for a client. I want to write both a Windows based WPF application and a Web based version. I want to use the same set of classes if possible, if not, then at least with little modification.

I read a couple of articles, but I am not following the architecture and the high-level concepts of .NET 3.5 & 4 discussed there. I want to move step-by-step by designing only what I really need in my real-life project.

Is there any easy step-by-step reference to MVVM? Is MVVM a super-set or a sub-set of MVC? Which pattern is modern and which one should I choose for Windows & Web versions of my application?

There are certain classes which I rarely need to connect with the View. In that case, designing the same class in the MVVM way will prove to be an added labor.