Cook the sliced potatoes in slightly salted water until just barely tender then rinse and drain them.
Put them in a bowl while still hot and pour the ½ cup of vinaigrette or Italian salad dressing over them. The heat helps the potatoes to absorb the flavor of the dressing better.
Let the potatoes marinate in the refrigerator for about two hours, then lift them out of the dressing.
In another bowl, blend together the ½ cup of sour cream, the ½ cup of mayonnaise, the 2 teaspoons of horseradish, the 3 crumbled slices of bacon, the 3 tablespoons of pickle relish, the 3 chopped green onions, the 2 tablespoons of chopped dill and the salt and pepper to taste.
Blend all of these ingredients together and then fold in the potatoes, refrigerate for at least two hours to chill and serve.