when i press left mouse button down and drag it over any screen area, i want to highlight this area with color, until i release my left mouse button. and of course, i only want this to be temporary,i.e as soon as i click my mouse elsewhere, the highlighted area is gone.

now my problem is highlighting the screen area. i can get the mouse curr position, then what message should i overide and how to in order to highlight the area as my mouse drag over it?? i appreciate a simple sample codes.. preferably with win32