LIMITED POWER OF ATTORNEY

The undersigned hereby appoints each of
Raymond G. Smerge, Paul M. Johnston and Anita L. Nesser as his
attorney-in-fact with full power to act in his name, place and stead for
the limited purpose of executing on his behalf all forms required to be
signed and filed by him under Section 16 of the Securities Exchange Act of
1934 and the rules and regulations promulgated thereunder.

IN WITNESS
WHEREOF, the undersigned hereunto sets his hand this 20th day of July,
2004.

James J. Postl