"Vampire!" The very word conjures up visions of ruined castles, of enigmatic, pale-skinned noblemen shrouded in dark cloaks, of slumbering beauties being bloodily ravished by supernatural, nocturnal creatures. But just how accurate is that picture? How much do we really know about these mysterious entities? Surprisingly, perhaps, almost every culture can boast of its own vampire beings, few of which correspond to the stock Hollywood image-some are not even human in form, some do not drink blood, some appear in daylight.