<PAGE>   1
 
                                                                      EXHIBIT 24
 
                               POWER OF ATTORNEY
 
     We, the undersigned hereby constitute James P. Connolly and Charles W.
Cramb, or either of them, our true and lawful attorneys with full power to sign
for us in our name and in the capacity indicated below the Annual Report on Form
10-K pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934,
filed for the Company with the Securities and Exchange Commission for the year
ended December 31, 1998, and any and all amendments and supplements thereto,
hereby ratifying and confirming our signatures as they may be signed by our said
attorneys, or either of them, to said Report and to any and all amendments and
supplements to said Report.
 
     WITNESS Our Hand and Seal on the Date set forth below.
 
<TABLE>
<CAPTION>
                     SIGNATURES                                        TITLE                       DATE
                     ----------                                        -----                       ----
<S>                                                    <C>                                    <C>
 
                   ALFRED M. ZEIEN                             Chairman of the Board          March 18, 1999
-----------------------------------------------------  of Directors, Chief Executive Officer
                   Alfred M. Zeien                                 and Director
 
                  MICHAEL C. HAWLEY                     President, Chief Operating Officer    March 18, 1999
-----------------------------------------------------              and Director
                  Michael C. Hawley
 
                  CHARLES W. CRAMB                         Senior Vice President, Chief       March 18, 1999
-----------------------------------------------------          Financial Officer and
                  Charles W. Cramb                         Principal Accounting Officer
 
                  WARREN E. BUFFETT                                  Director                 March 18, 1999
-----------------------------------------------------
                  Warren E. Buffett
 
                   WILBUR H. GANTZ                                   Director                 March 18, 1999
-----------------------------------------------------
                   Wilbur H. Gantz
 
                 MICHAEL B. GIFFORD                                  Director                 March 18, 1999
-----------------------------------------------------
                 Michael B. Gifford
 
                  CAROL R. GOLDBERG                                  Director                 March 18, 1999
-----------------------------------------------------
                  Carol R. Goldberg
 
                  HERBERT H. JACOBI                                  Director                 March 18, 1999
-----------------------------------------------------
                  Herbert H. Jacobi
 
                   HENRY R. KRAVIS                                   Director                 March 18, 1999
-----------------------------------------------------
                   Henry R. Kravis
 
                 JORGE PAULO LEMANN                                  Director                 March 18, 1999
-----------------------------------------------------
                   Jorge Paulo Lemann
 
                RICHARD R. PIVIROTTO                                 Director                 March 18, 1999
-----------------------------------------------------
                Richard R. Pivirotto
 
               ALEXANDER B. TROWBRIDGE                               Director                 March 18, 1999
-----------------------------------------------------
               Alexander B. Trowbridge
 
                  MARJORIE M. YANG                                   Director                 March 18, 1999
-----------------------------------------------------
                    Marjorie M. Yang
</TABLE>
 
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