Incoming -- would the nations of the world work together?

Contemplate this; an asteroid is spotted and computed to be on an intercept/impact trajectory with Earth. Would there be a haphazard, every-country-for-itself response to the potential impact, or could the nations of the world band together to launch (real or figuratively) a program to deflect the rogue rock?

That's what the workshop was about:
Workshop Emphasizes Need for International Response in Dealing with Earth-Threatening Asteroids

"The workshop brought together for the first time space agencies to discuss the future deflection of a hazardous asteroid, said former shuttle astronaut, Tom Jones, Chair of the Association of Space Explorers (ASE) Committee on Near-Earth Objects.

“Representatives from NASA and the European Space Agency, facilitated by Secure World Foundation and the Association of Space Explorers, talked substantively about how their programs could be coordinated to gather important planetary defense knowledge about asteroids, what asteroid research is needed to facilitate deflection planning, how space agencies should demonstrate asteroid deflection technologies, and when future planning meetings should take place,” Jones said.

moving on down the piece a bit:

Taking a leading role in the workshop was Sergio Camacho, space science researcher, former Director of the UN Office for Outer Space Affairs and now Secretary General of the Regional Centre for Space Science and Technology Education for Latin America and the Caribbean (CRECTEALC).

Camacho assisted in defining future planning tasks and studies for the MPOG that will later be merged with findings of other experts to create a final report to the UN committee. Such a report will recommend how to react to an impact threat from a Near Earth Object, or NEO.

Now, here's my question. What would happen if TOMORROW (that would be November 6, 2010), a telescope spotted a 100-meter asteroid with a 100% certainty of impact on June 12, 2011? Astronomers quickly determine that, given orbital uncertainty, the impact will take place close to the southwestern coast of Australia (and might hit it). Perth and environs would be most at risk.

What would we, collectively as nations and humans, do about it? Would we go the Armageddon route, or just hope it smacks ocean and get ready to mitigate?