Cook the pasta. When pasta is cooked to taste, drain and place in a separate bowl large enough to hold the entire salad. In a small bowl, mix oil and vinegar with salt and pepper. Set aside. Meanwhile, prepare the arugula, radicchio, cheese and walnuts. Add dressing and mix well. (Adding the dressing to the warm pasta helps it absorb the flavors more.) Add the cheese (also while pasta still warm, help it melt slightly.) Add the radicchio and arugula, toss. Sprinkle walnuts on surface. You can either serve it immediately, refrigerate for an hour or so or if preparing it several hours ahead of time leave out the radicchio and arugula till last hour or last minute.