Drain pineapple, reserving juice; set pineapple aside. In a small saucepan, combine the gelatin, water and reserved juice. Cook and stir over low heat until gelatin is dissolved. Refrigerate until syrupy, about 30 minutes.
In a small bowl, beat cream cheese until fluffy. Stir in gelatin mixture, marshmallows, walnuts and pineapple. Fold in whipped topping.
Transfer to a serving bowl. Cover and refrigerate for 2 hours or until set.