highlight screen area as mouse hold down and drag over

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

when u get the mouse over a control, grab its handle by WindowFromPoint()
take its rect by using GetWindowRect()
draw a rectangle in that area with any color for a while, remove the rect, and redraw again remove again... repeat this as long as u want.

check this and the references in this article this will give you a more clear picture.
hope this helps