ALTHAM - The Celtics are in full playoff mode, and it has nothing to do with some members of the team staying after practice yesterday to watch the conclusion of the Pittsburgh-Baltimore NFL game. Better basketball is the Celtics' main focus. The playoff atmosphere at the FleetCenter comes courtesy of Boston's next three opponents - the Raptors, the Pacers, and the Sixers. All three played in the postseason last season and hope to return.