What can one do in the following situation:  My neighbor, who works
for a collection agency and who has some personal issues with me,
obtained access to my social security number.  He referenced it in a
letter (on his company letterhead) regarding a non-financial matterto
the Board of our condo association.  He had no legitimate reason to
access my information.  My question is whether there exists a federal
law against thios sort of thing, or is it merely harassing and rude? 
And if there is such a law, what should my next step be?  Thanks for
any help you can provide...

Hello Glitterspank-ga,

I spoke with my local Social Security office about your situation.
When I explained it to the representative, she was horrified. She
advised me that not only did this incident more than likely violate
privacy act laws, that it probably violated agreements your neighbor
had with his company about client information confidentially, and as
the commenter suggested below, violated federal/state regulations set
for the collection agency your neighbor works for as well.

She stated your next step should be to contact a local lawyer ASAP and
to make sure you have all documentation of this incident you can get
your hands on. How you found this information out, a copy of the
letter if possible, any times and dates of conversations, phone calls,
and to be as accurate as possible. If you have any further questions,
she suggested contacting your local Social Security office, which you
can do by zip code locator here:
http://s3abaca.ssa.gov/pro/fol/fol-home.html

In addition, here are five places you could find a local lawyer in your area.
http://lawyers.findlaw.com/
http://www.lawyers.com/?site=466&cmp=KA20068
http://www.findalawyer.us/
http://www.legalmatch.com/bd/intro1.html?keyword=find+a+lawyer&engine=adwords
http://dexonline.com/servlet/ActionServlet?pid=changeLocation&cityText=&from=&catType=BROWSEHREF&surroundingAreas=true&headingID=13h1&queryType=HEADING&headingName=Legal

Searches used:

Google.com
Social Security Office
://www.google.com/search?hl=en&ie=UTF-8&oe=UTF-8&q=social%20security%20office&btnG=Google+Search

Google.com
Find a lawyer
://www.google.com/search?hl=en&ie=UTF-8&oe=UTF-8&q=find%20a%20lawyer&btnG=Google+Search

Dexonline.com is a phone book site I already knew of.
If this answer requires further explanation, please request
clarification before rating it, and I'll be happy to look into this
further.
Nenna-GA
Google Answers Researcher

This is identity theft.  Or at the very least it is unlawful abuse of
collection agency files.  I recommend you contact the FTC (the agency
who deals with this).  Their hotline is 1-877-IDTHEFT to talk with one
of their counselors. Even if your neighbor is being rude and
vindictive you can return the favor by having the FTC do a full
investigation (hey, they may find he's doing this to others as well)..

Hope this helps

Likely illegal, but not identity theft.  That would involve posing as you.