When Chief Justice Rehnquist retires, the president will have the option of appointing someone directly to the Chief Justice's position or of appointing another associate justice and moving one of the current justices to the CJ spot. I won't be at all surprised if the president nominates Alberto Gonzales to the next Rehnquist vacancy but promotes Justice Thomas to the Chief Justice's position. That move would require two confirmations instead of one, but it could be a good move all around.
Bill
I see something like that, but Scalia becoming The Best CJ in history