Don't be fooled by the poster pimping funny Englishman Simon Pegg, the clever bugger who helped bust open the zombie canon (Shaun of the Dead) and sent up the action-cop genre (Hot Fuzz). This romantic comedy is strictly by the book: Dumb guy (Pegg) loses perfect girl (Thandie Newton), who then finds a new man (Hank Azaria), who seems awesome but is revealed to be a cad. So, the two men take to battle, in this case, running a London marathon, in order to prove ... well, something. There's the odd chuckle, but these two funnymen plus Irish-comedian co-star Dylan Moran deserve a sharper script and a less hackneyed story. (Which also features, in the seen-too-often department: extra-cute kid; goofy Indian neighbor; upscale cupcake bakery; short-shorts jokes.) Former Friend David Schwimmer makes his directorial debut. Starts Fri., March 28. (AH) [capsule review]