Have eight (1/2 cup) molds ready. Remove ice cream from freezer and allow to soften at room temperature.
Put the gelatin in a medium bowl. Stir in the boiling water with a whisk until gelatin is dissolved. Whisk in the cranberry sauce until well blended. Stir in the vanilla ice cream until no white streaks remain. Ladle into the molds. Refrigerate for at least 4 hours or until firm.
TO UNMOLD: Dip the bottoms of the molds in warm (not hot) water. Invert onto serving plates and, holding both the molds and plate, shake down sharply to release molds. Repeat, if necessary.