Transportation in Hanoi
There are plenty of taxis and minibuses plying their trade between the airport and city centre, and it's possible to hire either for a trip around town. Renting a car or motorbike is a popular option, despite the presence of water buffalo, chickens, maniacal truck drivers, bicycles laden with struggling pigs, and packs of hormone-crazed teenage boys in vehicles of every shape, size and color all sharing the narrow, pockmarked roads and obeying traffic laws that have no parallel in the known universe. Hanoi is so compact that you can get by (and get fit) by walking around town. Remember, walk don't run through the traffic: the drivers will go around you (just don't try this at home!).
Apart from walking, motorbikes and scooters are the most common way for the locals to get about. Travelers can easily rent, with or without a driver. They're fantastic fun - in a suicidal sort of way. Consider riding with a local guide for a day or two before going it on your own.
Buses are cheap, but confusing to use, with numerous schedules and routes and not particularly good signage.
Bicycles are another good way to navigate Vietnam's capital. You can rent anything from leaden Chinese road warriors to high-tech Japanese mountain bikes, perfect for weaving around those potholes and farm animals. Hanoi is strictly BYOH: Bring Your Own Helmet.