How so?
Because he gets ONE new justice for O'Conner, TWO Scalia gets promoted to CJ instead of Rehnquist, THREE he gets to appoint another new justice to take Scalia's old spot. One, two, three solid conservatives, plus Thomas.
Now, if Stevens, Ginsburg, Kennedy, or Souter retires (or dies) he gets FOUR, FIVE, SIX & SEVEN. Wouldn't that be sweet? Breyer would have to write all the dissentions.