Good mods for learning 3D2D Cursors from?

Im looking for an addon which has a simple 3D2D cursor on it. Just something small so I can learn how to do it. I have actually gotten as far as making the cursor and making it follow the aimpos but im struggling with what needs to be done bounds wise. PCMod2 I have heard is 3D2D but id rather have an addon which is a little smaller.
Or if anyone can post some sample code id be deeply greatful.