We just returned from a two-week tour of northern Vietnam, with the itinerary planned by Win An Tours. It featured a mixture of biking, hiking and kayaking; traveling was by boat, train and bus. Every detail was planned yet flexible. We visited a national park, the Sapa region (the "roof" of Indochina) and the Ha Long Bay area. Our guides were helpful, knowledgeable and entertaining.
Win An Tours, Hanoi, Vietnam; http://www.winantours.com