I am interested in getting clear guidance on what is legal and illegal
when posting to stock message boards, to the rest of the Internet, and
even if legal, what will engender lawsuits.

What I (think) I know is summarized in one sentence:

Posting your opinion to a message board and on the Internet is legal,
a form of protected speech, even when securities law is invoked.
(for example, see http://news.com.com/2HRS2GO+Court+ruling+a+boon+for+stock+message+boards/2100-12_3-261878.html,
I don't think it was appealed.  There are many more cases and better
evidence than this, I'm sure)

However, it really is more complicated than that.

I read the content on these two links (and many others) and they were
as confusing as enlightening.  Granted, they may have been written by
lawyers with an interest in promoting securities law work, but still.
http://www.kentlaw.edu/classes/rwarner/legalaspects_ukraine/securities/overview.htm
http://www.cybersecuritieslaw.com/articles/Litigation.htm

For example, I may have posted something to a message board in good
faith believing it was true, but it ends up being false or unprovable.
 According to the above pieces, and other things I have read, a
company could decide to sue based on my knowingly making false claims
and/or libel and/or some other securities law.  And win. Win if I had
crappy defense, didn't have money for defense, had a bad jury or judge
overseeing the case, seemed like I "knew too much about investing",
seemed like I was worth suing for the money, or to make sure I would
shut up, etc.

Scenario two.  What if I believe I have information that can
negatively (or positively) affect a company and its share price.  I
have collected it from public sources, organized it in a particular
fashion, and then published it on my own web site.  That alone might
lend itself to corporate scrutiny.  For a negative publication, a
company might claim libel, even if I tried to be careful not to make
additional claims beyond what I found OTHERS had claimed or found in
good reference material.  But, what if I decide to make stock trades
based on that information?  Would it further make a difference if I
actively went to to stock message boards like those at
finance.yahoo.com and The Motely Fool (www.fool.com) and informed
people that I had published this information?  Are there protective
measures I could take to reduce the chance of lawsuits or other
harassment?

I am asking because I would like to carry out these activities with
the knowledge that I am within the law, and have indemified myself as
much as possible against legal action.

Why do I care quite so much?  Two reasons, the SEC and corporations. 
First, the SEC took legal action against Jonathan Lebed, a 15 YEAR OLD
for pumping and dumping equities with message boards as his primary
communications tool.  They used him, instead of any real adult in the
brokerage industry, as their criminal
(http://www.cs.brown.edu/people/rbb/risd/Lebed.html) .  More recently
the SEC has pursued a few high profile examples such as Henry Blodget
(http://www.sec.gov/news/press/2003-56.htm) and Frank Quattrone, but
that first example, a civilian using message boards, still has me
concerned.

Second, corporations, which consistently bitch and moan and pursue
legal action against individuals on a regular basis.  Whitney Tilson
has gotten in trouble with the Troy Group
(http://kip2.kiplinger.com/magazine/archives/2005/03/feinbergfull.html)
and Overstock has begun to rail, and take legal action against, naked
shorts, the "Sith Lord", and others for defaming and somehow
damaging(?!?!) the company.  SLAPP and intimidation lawsuits
(http://www.casp.net/cyberslapp.html) are proliferating (or are they?)

I am hoping for an answer tailored to the general investing public,
NOT for someone with Series 7 or other brokerage licenses, ties or
official investing certifications.  Those credentials come with their
own codes of ethics and rule systems which complicates (and reduces?)
what one is allowed to do.  The answer might include particular laws
which one needs to be aware of, what kind of defensive strategy to
use, disclaimer writing tips (when are disclaimers necessary and/or
recommended?), case law and other legal precendents, anecdotal
thresholds for what will draw the attention of a regulatory body or
corporation (shares traded, market capitalization loss, how bad the
news is, who publishes it), etc.  Any articles, texts, or even online
message threads adding further color to the answer would be
appreciated.

Finally, I know there are plenty of lawyers who handle cases on the
side of corporations.  However, are there law firms that specialize in
representing individuals in cases such as these?  Has the Electronic
Freedom Foundation ever handled a question like this?

In order to limit my question, I do not need information on online
chat, instant messaging, and other unthreaded, unarchived
communications, unless you have easy access to such information.

As I get feelers and requests for clarification on this question, I
will be open to rephrasing, breaking the question, narrowing and/or
widening the scope, etc.

Additional References:

SECs thoughts on message boards
http://www.sec.gov/answers/msgbd.htm
From corporate POV for protecting reputation, business on net
http://www.abanet.org/buslaw/blt/blt9-eisenhofer.html
Simple page about libel
http://www.cyberlibel.com/libel.html
Interesting material for scaring into use of anonymous email address
http://www.johndoes.org/html/dewey.html
Law firm talking about what to do about internet "problems"
http://www.realcorporatelawyer.com/faqs/msgboards.html
Ruling against a Motley Fool UK user
http://www.theregister.co.uk/2005/03/24/motley_ruling/