Line the bottom and two long sides of a 9 x 5 x 3 inch loaf pan with waxed paper.
Trim the crusts from the pound cakes, and cut each cake lengthwise into 3 even slices. Line the bottom and long sides of the loaf pan with 3 of the pound cake slices. Trim two of the remaining slices to fit the short ends of the pans, and reserve the scraps.
Pack the sherbet into the cake lined pans, and top with the remaining slice of cake. Use the cake scraps to fill in any areas with exposed sherbet. Cover the cake with waxed paper. Freeze until firm, at least 3 hours.
In a mixing bowl, combine cream, sugar, and vanilla; beat until stiff. Invert cake on serving platter, and frost with sweetened whipped cream. Return cake to the freezer until ready to serve.