Focusing a window for scrolling

I have some experience in Python and Java, but I dont really know the .NET framework and how to interact with Windows. What I want to do is a little program/script (maybe I need a DLL?) that when I use the scrollwheel on my mouse, the program that is right under the pointer gets focused and scrolled. Sometimes I scroll, and because another program is focused then I have to click开发者_JS百科 on the program and then scroll. Its not that annoying, but I just want to learn how I would accomplish that in Windows environment.

Well, not exactly the Katmouse program, but to get a start i suppose you could look at this and the tutorial for that

You might also wanna look at the new System.Reactive stuff in .net 4, i have seen people do some neat things with it. Here's one example