Zlata Filipovic is a thirteen year-old Sarajevan, whose diaries of the war in Bosnia have been published this month as "Zlata's Diary" (Viking). The book begins in August of 1991, with a new school year --fifth grade-- and the trappings of girlhood: piano lessons and tennis. By that spring, Sarajevo was under siege and Zlata's schoolmates were being killed, her family hiding in the basement and abandoned purebred dogs wandered the streets.