Quick question..

Question

How dificult would it be to define a region on the screen, such that you could capture mouse events that occured within that region only? Basically, I want to define a region aproximately 100 pixels high and 400 pixes wide. There may not be anything on this space (just blank desktop), or possible the background of another application. I just want to be able to capture mouse events that occur within the defined parameters. Would this be dificult to do? Thank you,