In a small bowl, combine the gelatin and cold water; let stand for 5 minutes. Add the boiling water and stir until the gelatin is completely dissolved. Place the bowl containing the gelatin mixture in the freezer for 15 minutes to cool.
Then, in a large bowl, combine the ground cranberries, granulated sugar, and marshmallows; let stand for 20 to 30 minutes to let the sugar dissolve. Add the gelatin mixture and stir well with a spoon. Add the grapes.
In a medium bowl, beat the heavy whipping cream with the vanilla and vanilla until stiff peaks form. Fold the whipped cream mixture into the cranberry mixture.
Rinse a 2 1/2 quart ring mold with cold water; do not wipe dry. Add the salad mixture, cover, and chill until firm, about 4 to 6 hours.
To unmold the salad, place the salad upside down on a serving plate. Rinse a clean kitchen towel in hot water and wring out thoroughly. Place the hot towel on the mold for a few seconds. Then hold the mold and plate together and shake gently. The salad should drop right out of the mold.
But if you fear trying to unmold a gelatin salad, just put the mixture into a 2-quart baking dish. Then you can cut the salad into squares and serve it that way. It's just as pretty, and much easier to make and serve.