EXHIBIT 23.6

                        CONSENT OF VINSON & ELKINS L.L.P.

         We hereby consent to the use in this Post-Effective Amendment No. 2 to
Form S-1 (File No. 333-85994) of our opinion, dated April 9, 2002, as to the
legality of the securities registered thereby (Exhibit 5.1 thereto) and our
opinion, dated April 9, 2002, as to certain tax matters arising in connection
with the securities registered thereby (Exhibit 8.1).

Dallas, Texas
April 23, 2003

                                              /s/ Vinson & Elkins L.L.P.