Add a caption button to all windows

Is there a way to register a new caption button so that it shows up on all windows?

I want to add a caption button to all windows that will cause the window to "maximize" to either the left or right half of the screen.

Thanks,
Chris

To do this, I would process the WM_NCPAINT message and draw the buttons when I draw the rest of the frame. Then WM_NCLBUTTONDOWN/WM_NCLBUTTONUP message processors that determine whether or not the "click" was within the area I had allocated to my new button.

I've never needed to do this, but that is how I would start - I may subclass the window if I found it to be necessary.