HOLLYWOOD, June 29, 2000 -- Mel Gibson's been a post-apocalyptic anti-hero, a half-cocked cop and a rich guy at war with kidnappers. But can he beat the redcoats? Can he beat George Clooney? It's a historic showdown of sorts at the box office this weekend. Gibson's "The Patriot" and Clooney's "The Perfect Storm" are the first two films with $100 million budgets, gigantic marketing campaigns and big buzz to face off over a summer holiday (namely, July 4 or Memorial Day). Already, "The Patriot" ha