When I post or answer questions on a discussion board I10 don't use my
correct name but they all come from the same ISP and computer.  Can
the discussion board manager determine where they are sent from and
then assume I am the same person.  It is not a large group, about 5
queries posted per day.

Several things can determine this. Most discussion board scripts can
track the IP address of the person posting the message.  However, most
ISP's use dynamic IP assignments, so it would be fairly uncommon
(depending on how large your ISP is) for you to have the same IP
address each time you log on.  Are you using dial-up or high speed
access?  One caveat is that the IP address will translate out and
typically, someone would be able to tell if a message came from the
same user for a couple of reasons:  1) The wording, grammar, and over
all style of the posts and 2) The IP address would be similar, ie, one
post would show 192.145.66.101 and another would show 192.145.66.80. 
No conclusive proof, but one could fairly guess that if the style is
the same and IP addresses were close, pretty good chance it was the
same person.

The other thing to watch for is cookies.  If the board is sending a
cookie, it can DEFINITELY know posts are from the same user.

-THV

Also see answers to my two posted queries 312531 and 312532.