Logan Airport (BOS) is a major international airport located across the harbor from Boston proper. It is serviced by 38 airlines, with direct flights from many European and American cities. Boston can also be reached by Amtrak trains and various bus lines (Greyhound, Chinatown, BoltBus, etc.)
Logan is well connected to the city by public transportation. MBTA (Metropolitan Boston Transit Authority) Silver Line buses make frequent stops at all terminals, and carry passengers to South Station where they can transfer to the subway system. There is no charge to go from the Airport into Boston. This page about the subway system explains how this all works.
The main conference venues (the NERD Center and MIT) are located in Kendall Square, Cambridge, across the Charles River from Boston proper. To get there, take the Red Line to the Kendall/MIT stop, it's a 5 minute walk. Two of the training venues (District Hall and Zipcar) are also best reached by the Red Line, get off at South Station, it's a 10-15 minute walk. The other training venue, Landmark Center, is very close to the Fenway stop on the Green Line's Riverside branch (D), but you can also take any Green Line train to the Kendall stop and walk 15 minutes down Brookline Ave.
It is unnecessary to rent a car while visiting Boston; in fact we recommend against it unless you are planning an excursion to the New England countryside. The public transportation system is good, the parking is difficult, and the drivers are crazy.
Some parking information may be available from the various venue web sites: Microsoft NERD, District Hall, MIT, MIT Media Lab, Zipcar offices, Landmark Center. You may also be able to locate parking using the Google map links on the training locations page. Be prepared to spend $20+ for a few hours of parking and to encounter traffic, confusing one way street layouts (with possible GPS failures), and aggressive, unpredictable drivers.