After she and husband Michael Douglas dropped out of “Monkeyface,” Catherine Zeta-Jones has emerged as a front-runner to join Brad Pitt in the Regency Enterprises film “Mr. and Mrs. Smith.”Nicole Kidman had been set to play the “Mrs.” until her “Stepford Wives” schedule created a conflict. Regency sources have said Kidman isn’t completely out of the picture, though it is known they are looking to firm an actress to keep Pitt in place for an early fall start. Zeta-Jones is coming off an Oscar-winning perf in “Chicago” and would make a strong fit in this Doug Liman-directed drama about a pair of married assassins assigned to kill each other. Simon Kinberg wrote the script.