Bad news for Renée Zellweger: The ''Cold Mountain'' costar is the early front-runner in a race that the early frontrunner almost always loses. On paper, she seems all but a lock: A win would allow the Academy to grant her a consolation prize for losing to Nicole Kidman in last year's Best Actress race, and her ornery farm girl in ''Mountain'' was a scenery-chompin' standout. Only problem: ''The Academy'' doesn't pick winners -- voters do, and they love to upend expectations. The wrenching work of ''Thirteen'''s Holly Hunter and ''Mystic River'''s Marcia Gay Harden would probably make them strong contenders if both hadn't won before, and first-timer Patricia Clarkson seems destined to win eventually -- but for a stronger movie than ''Pieces of April.'' That leaves one possible upset winner: Shohreh Aghdashloo, whose work as a frustrated wife in ''House of Sand and Fog'' has knocked out moviegoers -- and don't discount the potentially history-making impact of honoring an Iranian actress. We'll give Zellweger the edge, but barely.