Ugh, February? That's sort of the worst time to be here. Late September - early October is much nicer. February is just a mess.
First rule: Take public transportation (MBTA, use the trains and subway mostly) everywhere you possibly can. The subway mostly drops you off within 3 blocks of anywhere you want to go anyway. Do not get a rental car. Do not drive. Boston area is just not for driving. The commuter rail can take you to outlying towns, and if you want to see the touristy stuff (although now is not a good time for touristy stuff) there are generally charter trolleys and buses and things that circulate or can be arranged. Really really do not drive. When friends and relatives visit, they persist in this notion that somehow, since I live here, I have the Secret Of Driving In Boston. I tell you, no. Take the train. No one around here drives if they can possibly avoid it. This time of year especially, you will want to stay indoors and see indoor things, which are all along the subway lines. Your friend can pick you up at the airport or the train station if need be.
There is no parking in Boston for less than $20/second. There never will be. The roads are narrow and confusing and there is nothing to be done about it. Pieces of the Big Dig could collapse on your car and kill you dead. Don't drive in Boston.
Indoor things to do: Museum of Fine Art on the Green E Line is quite nice. Quincy Market on the Green Line at Government Center is a big shopping/food thing and probably the only place you'll find a meal for less than $15. Prudential Center is another big shopping thing, also on the Green Line. Blue Man Group is perpetually playing at the Charles Playhouse (Green Line @ Boylston). The science museum is rather nice (Green Line @ Science Park). Looks like Haavaahd is giving a few concerts in Feb--a Mendelssohn organ recital, a gospel-style concert, plus they also have several art galleries that are open to the public (Red Line, Harvard).
Food: Lobsters are going pretty cheap right now, for lobster. Oysters, I am told, are also rather good around here, although I don't eat them raw.
If you absolutely insist on driving, against all advice to the contrary, then the best thing I can tell you is to not visit Boston itself and instead stay in the little Tourist Towns. We have oodles of these: Salem, Lexington, Concord, Wellesley, Ipswich, Gloucester, Marblehead, Hingham, you can't move without tripping over overpriced and adorable bits of architecture. They typically have at least one historical site where Paul Revere once hitched his horse or something, but they also have someplace to park for somewhat less than highway robbery. Salem has the Peabody-Essex Museum, which is rather nice and surprisingly large--it's mostly about boats and shipping trade with the Far East. They also have a big replica tall ship that you can tour, and a few colonial buildings that are open to the public for, hmm, I think it was $5 last time I went. For little bitty tourist towns with stuff to do, Salem is probably my favorite because everything there is pretty cheap, there is parking by the museum, their Visitor Center in the armory has a bunch of maps, they have a good microbrewery in the middle of town (Beer Works) and there are several things to do as well as the museum and house tours. And there's a candy shop across from the House of Seven Gables that sells the best saltwater taffy ever.
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