In a food processor or blender, puree the pineapple with the sugar, transfer the puree to a small saucepan and add the rum.Bring the mixture to a boil and boil it, stirring occasionally, for 7 to 10 minutes, or until the excess liquid is evaporated and the mixture is thickened. Chill the mixture in a bowl, covered, for 1 to 2 hours, or until it is cold. In a chilled bowl beat the cream until it holds stiff peaks and fold it into the pineapple mixture gently but thoroughly. Divide the fool among 9 stemmed dessert glasses and serve it chilled. Garnish with 2 or 3 whole strawberries which have been soaked in rum.