It isn’t easy to accept Diane Keaton as a brittle, high-powered executive, and it’s even harder to believe she’d throw away her boyfriend and career for the sake of a 13-month-old baby girl she inherits from a long-lost cousin. This, however, is the kind of Hollywood comedy that wants to have everything both ways, to give us a character who decides not to play the game and who wins all the chips just the same. Producer Nancy Meyers and director Charles Shyer collaborated on the fanciful and unconvincing script; Keaton does her best, which is unfortunately not enough, with the fatal miscasting. With Harold Ramis, Sam Wanamaker, and Sam Shepard, the latter as an amiable New England veterinarian who more or less plays Annie Hall to Keaton’s Alvy Singer. (JR)