^ User was perma-banned for this post.
Technically you aren't supposed to import here without a permit from the Dept. of Health, like any other therapeutic drugs or equipment, in reality nothing will probably come of it... in Australia.
I do know that under Australian law, a DXM product with more then 600mg of DXM contained therein is a S4 substance; so importing a gram of powder would be importing a prescription only drug. This is Australian law however, NZ may be different but I assume their scheduling of DXM is probably similar. I am also not too familiar with NZ Customs requirements, you may want to check out their website and do some reading on importing therapeutic substances.