Going to Billerica (which I believe is about 25 miles from the center) with work at the end of the month and will have a day and a half to myself and was looking for advise on what to do, where to go ect?
Will you have a car or some means to get downtown?
If so, you'll want to have a walk around the Back Bay neighborhood up to Boston Common and then over to Fanueil Hall marketplace. Definitely get yourself an Italian dinner in the North End. Take the T (the underground) over to Harvard Square and have a look around. You could do a Boston Harbor cruise if you've got time (I believe there are ones that last a couple of hours, show you various sights).
That should keep you occupied for about a day and a half... let me know if you want more ideas