Depending on how you feel about the Purple One, Barney"s Musical Castle is either a loathsome marketing tool (a self-addressed piece of video fan mail, sort of) or a magnificent 70-minute romp for young minds. The tape plants viewers in the audience for a performance of Barney"s third live stage show, a cross-country affair for which more than a million of the warm-fuzzies-inducing big fellas turned out. The story"s simple: Barney and his usual complement of sidekicks (a handful of completely nonironic, overly nice school kids, plus the brother-sister dino duo of B.J. and Baby Bop) discover a lost crown in the flimsy-looking set they call the Enchanted Forest and set out to return it to the king. Their mission is interspersed with syrupy, kid-pleasing song and dance numbers (20 of them total). To gain entry to the king"s castle, for instance, the gang must perform the musical equivalent of a password. That"s a song, the guard explains, that involves clapping, foot-stamping, and shouting hooray! (Barney to the crowd: "Do we know a song like that?") Throughout the performance, the camera cuts away to shots of singing, clapping, overjoyed toddlers, and their delighted-looking parents, most of them gripping, wearing, or waving some article of Barney paraphernalia. Buy the video if you"ve disappointed a young devotee of the dinosaur by skipping the show when it blew through your town or if the king of cornball makes your kids happy. Ages 3 to 6. --Tammy La Gorce