Fennel with Mussel Salad

1-1/2 pounds red potatoes
48 fresh mussels, scrubbed and debearded
1 fennel bulb with stalks, (1-pound)
1/2 cup sherry vinegar
3 tbsp diced red onion
1 tbsp finely chopped fresh tarragon
2 tbsp olive oil
3/4 tsp salt
3/4 tsp pepper
3 cloves garlic, minced
2 med tomatoes, cut into wedges
6 cup torn romaine lettuce
2 cup torn radicchio
2 hard-cooked eggs, quartered lengthwise

Place potatoes in a saucepan; add water to cover, and bring to a boil.
Cover; reduce heat, and simmer for 15 minutes or until tender. Drain and set aside.
Steam mussels, covered, 10 minutes or until shells open; discard any unopened shells.
Trim tough outer leaves from fennel. Dice stalks to equal 1 cup; set aside.
Cut fennel bulb in half vertically; discard core. Cut each half crosswise into thin slices to measure 1/2 cup, and set aside. Reserve remaining fennel for another use.
Combine vinegar and the next 6 ingredients (vinegar through garlic) in a large bowl, and stir well. Reserve 1/4 cup dressing; set aside.
Add potatoes, mussels, fennel, and tomato wedges to bowl; toss gently to coat. Cover and chill 30 minutes.
Combine reserved 1/4 cup dressing and greens in a bowl; toss well.