Jason Kidd’s wife had just given birth to twin girls, so he was a late arrival to Nets training camp in 2001. Still, he attended the team dinner the night before the real work began. Coming off a typically dreadful 26-victory season, Nets coach Byron Scott addressed the players. When he was finished, Kidd asked if he could say a few words. “He said, ‘We’re going to the playoffs,’ ” Lawrence Frank, who succeeded Scott as coach, recalled yesterday after Kidd announced his retirement following 19 brilliant NBA seasons. “The guys in the room didn’t know what they were hearing.” “Nets” and “playoffs” were two words that prior to Kidd went together like “jelly” and “liver.” Kidd soon repeated the promise to the media. People thought Kidd was nuts. “The minute he walked in the door, you could feel the entire mood change,” Richard Jefferson said. “You could feel the air in the gym completely change.” Change. That was the word. Kidd changed everything about the Nets. The sad sacks became NBA finalists, not once but twice. There were better teams, but has there ever been a more entertaining team than the group that featured the blinding quickness of Kidd and Kerry Kittles in the backcourt, Jefferson and Kenyon Martin up front? “His toughness, will, desire, heart — whatever you want to call it — that was what made Jason special,” said former Nets and current Sixers president Rod Thorn. “I could see him coaching or being a GM. He can run down every guy in the league. He has a terrific eye for talent. I’m sorry to see it end, but the overall body of work in his career is remarkable.“He set the tone every night. He was principally responsible for turning an entire franchise around.” Kidd did it with that will, with that desire, with that this-is-how-it’s-done attitude.