Preheat oven to 400�F.
Prepare macaroni & cheese as directed on package. While macaroni is cooking, cook meat with taco seasoning as directed on package.
Stir sour cream into prepared dinner.
Spoon half the dinner mixture into 8" square baking dish sprayed with cooking spray; top with layers of meat mixture, 1 cup shredded cheese and remaining dinner mixture. Cover.
Bake for 15 minutes; top with salsa and remaining shredded cheese. Bake, uncovered, 5 minutes or until cheese is melted.
For extra crunch and flavor, bake casserole as directed, topping with 1/2 cup coarsely crushed tortilla chips along with the salsa and remaining shredded cheese.