In a 2-1/2-quart soufflé dish or straight-sided serving bowl, arrange split ladyfingers around sides and over bottom of dish. Set aside.
In a saucepan, combine powdered sugar and unflavored gelatin. Add cold water and let stand for 1 minute to soften gelatin. Stir over low heat until gelatin dissolves. Remove from heat. Let stand for 5 minutes or until slightly cooled.
In a large bowl, combine the eggnog, vanilla, nutmeg, and rum flavoring. Stir in gelatin mixture. Chill until partially set (about 10 minutes).
Fold in the cherries and pineapple.
Beat the 1 cup whipping cream until soft peaks form; fold the whipped cream into eggnog-fruit mixture.
Turn mixture into ladyfinger-lined dish. Cover and chill for 6 to 24 hours. If you like, pipe more whipped cream around edge. Makes 12 to 14 servings.