We're going to Hanoi in October, so I'll be interested in details on your trip when you return.

A great series for walking tours, much better than Lonely Planet IMHO, are the Insight Pocket Guides. I bought Hanoi & Northern Vietnam (ISBN 981-258-045-X), which has nine city walking tours, three in the central city and six further out. Also has six suggested excursions, including Ha Long Bay. I agree with a previous poster that you should try to get there. We've not been yet, but a neighbor has and describes it as magical (as do most reviews). Book also has information on shopping, eating, night life, etc. and the walking tour maps are much better than LP.

Hanoi guide is $13.95 and includes a pull-out map of the city.