I'm a little confused. Rock Band is still not out in Australia, and there's no way to play copies of Rock Band on unmodded Aussie 360s, even if you import.
And yet, XBox Live Australia is advertising Rock Band downloadable songs on the Marketplace blade, specifically Maximo Park and the MTV2 Pack. Clicking the ad results in a "content not available" message.
Sounds like somebody's advertising dollars are not being well spent.