1. In a large pot of salted boiling water, cook the pasta until tender, about 8 minutes. Drain it in a colander, rinse well, and drain again.
2. Meanwhile, in a large bowl, whisk together the vinegar, water, salt, sugar, tarragon, and pepper. Add the oil in a stream, whisking until well blended.
3. Add the pasta and the remaining ingredients to the bowl and toss well. Serve the salad at room temperature. Serves 8 to 10.