I don't know of a way to get exactly what you described, but there are some Windows settings or 3rd party programs that can do similar, which may work for you depending on what you want to accomplish with this behavior.
Give a window focus without clicking:
There is a setting in Windows 7 which will activate any window (give it focus) just by hovering the mouse on it for a bit (used to be in the TweakUI package for earlier Windows versions). To access this in Windows 7, go to Ease of Access Center in the Control Panel. Click on the "Make the mouse easier to use" link and tick the box that says "Activate a window by hovering over it with the mouse".
Scroll on whatever window is under the cursor (without getting focus):
For this you will need a 3rd party tool. There are several out there which do it, but the one that I use is a free one called X-Mouse Button Control. This is great for if you have several windows open (on one monitor or across multiple monitors) and you want to scroll each of them independently without having to click on them each time before scrolling. X-Mouse Button Control can also be set to activate the window you scroll on. However, I use it without activating because I often want to scroll through a tutorial or StackOverflow without losing the place where I was coding on my other screen.