The University Operations Services, which administer things like on-campus parking and shuttle services, also has a resourceful website.
The T is run by the Massachusetts Bay Transportation Authority (MBTA) and is an easy way of getting around Cambridge, Boston and to and from Logan airport. The MBTA also runs bus services in the area.
Harvard University has a great deal for monthly bus and train passes, currently subsidizing 50% of the cost of a CharlieCard (MBTA-wide reusable pass). Check out http://www.commuterchoice.harvard.edu/transit/mbta/student_info.shtml for frequently asked questions and how to order your own pass.
The Commuter Choice Program at Harvard has more information on commuting to Harvard with information on Bicycling, Carpooling etc.
Zipcar, a provider of cars-by-the hour, is another alternative to owning a car in the Cambridge area. Harvard faculty, staff and students 21 years and older can join Zipcar for an annual fee of $25.
Parking on campus is extremely difficult and there are no university parking lots with parking spaces allocated to students.
Bicycling is big in the Boston area.
Check out Boston's official bicycling website with information on bike paths, bikes on public transit, bike parking and much more.
The Masschusetts Bicycling Coalition, MassBike, offers maps, tours and information on bike shops.