Mike Tyson's tiger, Zach Galifianakis' BabyBjörn and, of course, the photographs from the end credits are still burned indelibly in our brains. Next November we'll get more outrageousness from Todd Phillips, the director of "Hangover," and Galifianakis, who's reteaming with Phillips for a new R-rated comedy. Robert Downey Jr. adds extra star power as a father-to-be who, thanks to a series of unhappy coincidences, must drive across the country with a slacker (Galifianakis) to arrive in time for the birth of his first child. "We've made the most . . . movie about fatherhood," Phillips says. But don't expect a reprisal of Galifianakis' zoned-out man-child from "Hangover." Says Phillips: "There are still shadings of Zach and his humor, but it's an entirely different character."Melinda Sue Gordon / Warner Bros.