Unless things have changed very recently, the buses are only free for college students. That changed a few years ago, when the state reneged on a commitment to fund the PVTA and sent the money to pay for the Big Dig instead.
The best thing to do is to get your hands on the Valley Advocate, a free newspaper, that’s full of movie and concert and lecture listings.
@Lily: the place you’re thinking of might be the Iron Horse Music Hall, “the acoustic epicenter of the northeast”? Everyone who’s anyone in the folk and indie singer-songwriter music scene has played there, it seems. There’s also the Pearl Street nightclub, the Academy of Music (which has had financial issues, and may no longer have live music shows), and the Calvin Theater, all of which are excellent live music venues.