1In small bowl, mix cream cheese and horseradish. Spread about 2 tablespoons cream cheese mixture over each slice of roast beef.
2Cut each piece of roast beef crosswise into 12 strips. Roll each pickle half in roast beef strip. Refrigerate 1 hour (pickle-filled beef rolls will be easier to secure on toothpicks).
3For each, thread 1 tomato half on toothpick, then secure beef on pickle with toothpick.