Denman, I discuss some of this with GrapesOfWrath in the "Dark Star theory: a possibility or New Age drivel?" topic in the "Against the mainstream" section, as of Kaptain K pointed out.

To be brief, I don't believe Planet X exist, or any planets beyond Pluto in our solar system. The so-called gravitational perturbations of Uranus and Neptune were likely in error or caused the objects in the Kuiper belt.