“Grand Theft Auto IV” is the videogame event of the year, industry pundits swear. It is projected to sell 9 million copies on its Tuesday debut, besting the record set last autumn by Microsoft’s golden child, “Halo 3.” Wondering why there’s such frothing demand for a “murder simulator” that lets players live out their deepest, darkest fantasies–including hiring a prostitute, then beating her with a baseball bat in lieu of giving a tip? Can’t figure out why downtown New York has been painted black with “IV” posters? Here are our answers.