Other people go to the beach. But when you're as used to kicking bad-guy butt as ''Alias'''s Jennifer Garner, summer is no time to rest. That's why the newly-separated star is in New York City filming "13 Going On 30," a comedy in which she plays a geeky 13-year-old who gets locked in a closet by mean-spirited playmates, only to emerge from her entrapment suddenly all grown up -- and beautiful. (Think: a female version of Tom Hanks' ''Big.'')

