Today is the day when the question will be answered: Can two chart-topping, octave-jumping divas cut a tune without a catfight breaking out? The New York Daily News reports that temperamental songbirds Whitney Houston and Mariah Carey are heading into a New York studio to sing together for the first time. The strong-lunged singers will record "When You Believe," the theme song from the upcoming DreamWorks animated pic, The Prince of Egypt, which tells the story of Moses. Kenneth "Babyface" Edmonds will be on hand to referee, er, produce the single. The paper says that following the duet, Houston, who still shows no signs of breaking from troubled hubby Bobby Brown, will devote the next few months to recording songs for her upcoming album, her first since the 1996 soundtrack to The Preacher's Wife. Prince of Egypt, which features the voices of Val Kilmer, Ralph Fiennes, Michelle Pfeiffer, Sandra Bullock, Jeff Goldblum, and Patrick Stewart, among others, is due out Dec. 18.