Place the cake mix, Dream Whip, eggs, water, oil and vanilla in a large bowl. Beat until ingredients are incorporated.  Place the batter into a grease 13x9 inch baking pan. Bake the cake according to the cake box directions. Remove the cake from the oven to a cooling rack. Poke holes in the cake with a fork. Pour the sweetened condensed milk over the cake. Let the cake sit at room temperature for 3 hours, then refrigerate it.  When the cake is cold, frost it with the whipped topping.  The cake is at it's best left in the refrigerator for a couple days before serving.