There is something about the blender 2.5 & Durian to-do list that mentions adding lense flairs to the Blender internal renderer.
In the meantime I guess you are going to have to fake it or do it with 3rd party software, perhaps in the composite. I seem to recall After Effects can do lense flairs.
May I suggest a quick work around. If you have a camera trackto empty parent a halo material vert to it. If not then add one or parent it to the camera with an offset. Do a render layer with just this single vert and then do alpha over in the compositor.