Combine 7-Up and marshmallows in sauce pan. Cook over medium heat until marshmallows are melted. Add Jell-O, stir until dissolved, then add hot mixture to creamed cheese and beat until smooth.
Chill until almost set, approximately 30 minutes. Fold in whipped cream and Miracle Whip, then blend in pineapple and walnuts. Pour into a lightly oiled (or use Pam) two quart mold. Chill until well set.