Take a look at the list of tri clubs on the USAT New England web site:

http://www.usat-ne.org/

There is a link on the left for Tri Clubs in NE. I'd check the various web sites for the listed Boston area teams to see which ones might be of interest, then suggest posting back here with specific questions about specific clubs.

BrokenSpoke

Boston Tri Team, Team Psycho, Team Mercury Multisport, Tri-Fury and Team Envision (if you're a woman)

All have various open workouts and websites.

Cheers