Where can an individual post an opinion on unbalanced media coverage
of the war on terrorism that will be read by the world media?  I want
to have my say.

post your incisive and balanced commentary in a blog. 
This G****e service also offers a free Blogger service.  Start your own Blog.
Good blogs are sometimes cited by mediaplex talking heads and opinionators.

I don't know about "posting" but you could always contact various
"world media" outlets directly.

You could try Independent Media Center 

DESCRIPTIONL: "a collective of independent media organizations and
hundreds of journalists offering grassroots, non-corporate coverage.
Indymedia is a democratic media outlet for the creation of radical,
accurate, and passionate tellings of truth."

URL: http://www.indymedia.org/en/index.shtml