I have been looking for a quadtree/quadtree node implementation on the net for ages. There is some basic stuff but nothing that I would be able to really use it a game.
I warmly suggest you to use a rendering engine, Ogre3D for instance. As far as I know it supports Octrees for scene management. But you can extend the Octree-based class as you wish. I used to code the stuff I needed by myself, but for complex projects, it's just not the right way.