When police are alerted to a teenage drinking party in Darien, most of what they do revolves around the safety of the under-age drinkers there and the safety of other people who might be on the road when intoxicated drivers from the party go home. That was one of the themes brought up by two Darien police officers involved with youths in town when the officers spoke recently at a meeting for parents at Darien High School. Detective Mark Cappelli, who works on cases involving youths in town, and Officer Bryan Wallman, who had just been named (two days before the meeting) as school resource officer for Darien High School, replacing James Palmieri, who had just been named a detective. Cappelli, who grew up in town and lives here with his wife and daughter, has been on the Darien police force for 21 years, and on the Youth Bureau for the past nine years. Wallman has been a police officer in town for the past decade and previously was school resource officer at Hindley School.