I just found out that Roberto's Pizza in Greenfield and Montague has a couple Salvadoran items on offer as well. I had tamales in Greenfield the other night and they were excellent (less spicy than I'd like but what do you expect?). The cook said the Roberto's in Montague has pupusas, so I can't wait to go there!
If anyone has info about other spots for Salvadoran/Central American food in Western Mass. or southern VT (I actually live in Brattleboro) they would be MUCH appreciated!