In a small bowl let gelatine dissolve into water; set aside. Combine milk and 1/2 of the sugar in a small glass bowl. Microwave for 3 minutes or until milk begins to boil.
In a medium bowl stir gelatine mixture into the heated milk and sugar; gradually whisk in eggs using a wire whisk. Microwave mixture stirring with whisk after each minute until it thickens. Remove from microwave and pour in rum. Keep mixture refrigerated until it begins to set being sure to stir it occasionally as it chills.
In a medium bowl whip cream until soft peaks form; beat in remaining 1/2 of sugar. Set aside 1/2 cup of this mixture for garnish; keep refrigerated. Fold remaining whipped cream into microwaved mixture and pour into pie crust. Cover and refrigerate for 2 to 3 hours.
Serve with reserved whipped cream and a dusting of nutmeg.