"Dying is easy. Comedy is hard," English tragedian Edmund Keane supposedly said on his deathbed. Screwball comedy is harder still, however effortless such classics as BRINGING UP BABY and THE PALM BEACH STORY may make it look. Take two temperamental movie stars, Gwen Harrison (Catherine Zeta-Jones) and Eddie Thomas (John Cusack), who made a string of hits together before their golden romance degenerated into tabloid scandal and poisoned their careers. Add one egomaniacal director (Christopher Walken) who's holding hostage the only print of his new sci-fi opus, "Time Over Time," refusing to show it to studio executives before it's seen by journalists (a Hollywood no...