Days after the Littleton tragedy, Donna Ladd saw something in CompUSA that turned her stomach: piles of adult-rated, violent computer games such as Doom, Quake and Redneck Rampage on sale -- in the kids' section. Why don't mega-retailers such as CompUSA, Target and Media Play abide by the self-imposed video game rating systems? And why won't the software giants stop marketing violent crap to kids?