When we opened several windows, from one to another, click on it to display the desired window in 1st plan.
In Windows 7 or Vista, it is possible to move a window from 1 plan, just by pointing it with the mouse.
In Control Panel, select Ease of Access, then Make the mouse easier to use.
Check the Enable a window by hovering over the mouse, then click Apply.
It's an option that may prove useful for users with some disabilities, but also for all the users according to their habits.