A campaign has now been launched to raise awareness of this target -- currently we have over 380ppm of CO2 and it's going up faster than ever before -- http://www.350.org/
The Reality Report interviews Jamie Henn of 350.org, a creative new initiative formed following the scientific understanding that atmospheric greenhouse gas concentrations need to be reduced to at most 350 parts per million.
MP3: http://media.globalpublicmedia.com/RM/2008/05/Henn.Bradford.May19.08.mp3
http://globalpublicmedia.org/the_reality_report_jamie_henn
See also the Climate Code Red book and audio from earlier in the year -- this is essential listening and reading: http://www.indymedia.org.uk/en/regions/sheffield/2008/02/392071.html
And James Hansen's site: http://www.columbia.edu/~jeh1/
And the article on Real Climate on James Hansen's paper, Target CO2: http://www.realclimate.org/index.php/archives/2008/04/target-co2/