Using the Fit Special command, you can transform Y and X. Transformations include the following: log, square root, square, reciprocal, and exponential. You can also constrain the slope and intercept, fit a polynomial of specific degree, and center the polynomial.
To turn off polynomial centering, deselect the Centered Polynomial check box. See The Specify Transformation or Constraint Window. Note that for transformations of the X variable, polynomial centering is not performed. Centering polynomials stabilizes the regression coefficients and reduces multicollinearity.