Hmmm...
Personally I'd stay away from it strictly because of the sodium in the dressing mix (don't know what else is in the mix - the Hidden Valley website's nutritional/ingredient info must also be 'hidden' somewhere
Anyway - let's look at it this way - just did a search on the net and found the following recipe for ranch dressing from scratch - you'd probably be better off modifying this one - I'll put my suggested modifications in italics:
Ingredients
1/2 cup mayonnaise
1/2 cup sour cream
1/2 cup buttermilk
I'd substitute the first three ingredients with 1 cup cottage cheese, 2 Tbs fat-free mayo, 2 Tbs fat-free sour cream and 1/4 c buttermilk creamed together with a blender
1 tablespoon garlic powder
1 teaspoon dried oregano
1 teaspoon dried dill weed
1 tablespoon dried chives
1 tablespoon dried parsley
2 tablespoons grated Parmesan cheese
Since the 2 tablespoons of cheese is being divvied out into 12 servings, I don't see a problem keeping it in the recipe
1 dash hot pepper sauce
1 tablespoon Worcestershire sauce
1 teaspoon ground white pepper
Directions
Combine the mayonnaise, sourcream, buttermilk, garlic powder, oregano, dill weed, chives, parsley, parmesan cheese, hot sauce, Worcestershire sauce, pepper and refrigerate for at least 1/2 an hour. If the dressing is too thick, add a little extra buttermilk to thin.
Now remember, I haven't actually tried this yet...but it certainly looks doable to me!
You could also use fat-free plain yogurt in place of the ff sour cream...