The issue:
I want to arrange a chartered, guided van/bus tour that would take a
group of people (approx. 10-20) from a hotel in Nashua, NH (45 mins
north of Boston), drive them to Boston, MA, give a guided van/bus tour
of the city, and then drive them back up to Nashua.  This event is
being planned on a Saturday in August, 2004.

The questions:
1) What companies can do this?  Please give me several options and
their contact information.
2) How much will this cost?
3) If this is not possible, inform me of similar options that you may
have found during your research.

Please let me know if there are any clarification questions.

Hi Kevin - I'm a native Bostonian and should be able to help you.  I
will run with the assumption that you're OK with the group leaving the
van/bus to board another vehicle for the tour.  I say this as, while
finding the van may not be a problem, any sort of cultural/historical
perspective along with it may be difficult.  Be wary of who you
choose--the coach/bus/van industry is in general fairly competitive
and some if not most will tell you "Sure, we can do a cultural tour,"
only to find that Bob the Bus Driver just moved from Jersey last
weekend and doesn't know anything.

That aside, invariably any Bostonian would mention the Duck Boats
which, briefly, are amphibious vehicles providing a tour of the city
AND a little cruise on the Charles River.  Very popular and a great
intro to the city, if not slightly kitschy.  Any search on "Duck Tour"
will lend immediate results.

I'd add (lots) more but apparently I'm not an "expert," and thus am
not earning any "money" for my answer.  :)