In bowl, dissolve the jello in the boiling water and then stir in the strawberries, pineapple, bananas and nuts. Pour 1/2 mixture in a 9 x 11 or a 13 x 9 pan dish and refrigerate about 1 hour or until set. Set the remaining jello mixture aside.
Combine the sour cream, sugar and vanilla and mix well. Spread this mixture over the chilled jello mixture. Then spoon the remaining jello mixture over the top.