Marketing the feature-length action cartoon "The Incredibles" with a PG rating wasn't a sure bet, despite being the latest computer-generated opus from Walt Disney Co.'s hit factory Pixar Animation Studios. Sure, there was built-in want-to-see based on earlier animated Pixar triumphs "Toy Story" and "Finding Nemo." But Oren Aviv, 43, president of Buena Vista Pictures Marketing, could take nothing for granted. "I had to convince moviegoers that real human characters playing superheroes were as interesting, cool, fun and compelling as `X-Men' and `Spider-Man 2,' " he says.