Prepare pasta according to package directions. Set aside.  Cut grapefruit between membrane to release segments and reserve juice in separate bowl for dressing.  Prepare dressing combine grapefruit juice, vinegar, oil, lime juice and dill.  Combine pasta, celery, carrot, parsley and onion with dressing.  Cover and refrigerate for 1 hour if desired or until next day.  Arrange lettuce on plates and spoon pasta salad on lettuce.  Add salmon and grapefruit segments around salad and pour remaining dressing over salad.