I have decided that I want to use a 3D cursor in my game that hovers above the terrain. It will make picking very easy and look cool. But I need to know if the cursor is moved into a certain area that will cause it to be rendered onto the interface panel. Then the player can press buttons on the 2D interface on the side of the screen. I guess it would be the opposite of using the selection mode and name stack in opengl.

You already have the mouse cursor in window (x,y) coordinates so why not just test if it is in the box?