Sometimes the hard stuff comes easy and the easy stuff comes hard. Just look at the latest comedy from ”Shanghai Noon”’s Dey. The director had little difficulty convincing box office titans De Niro and Murphy to costar as cops who are cast in a reality TV show. But finding the right woman to play their producer? ”I wasn’t the first choice,” says Russo. ”’Showtime’ is in a lot of ways a goof on ‘Lethal Weapon’ and I think people had concerns that because I was in ‘Lethal’ that I wasn’t right. And De Niro went to bat for me.” So where does Shatner fit in? ”They need to be instructed on how to be a cop for television, so they hire this guy Shatner,” says the actor. ”As the guy who played T.J. Hooker, I teach them how to be flashy.” Ah, T.J. — seems like he’ll never get through with schooling those new recruits.