Cook the fettuccine according to package directions. Meanwhile, in a small saucepan, saute garlic in butter for 1 minute or until tender. Gradually stir in broth.
In a large bowl, combine the sour cream, whipping cream, salt and pepper; stir into broth mixture (do not boil). Drain fettuccine and transfer to a large serving bowl. Add the cream sauce, Parmesan cheese and walnuts; toss to coat.