AIM is discriminating against my location :/

I'm trying to create an account for AIM, but it requires me to enter a ZIP or postal code. That's easy enough, except for the fact that they've got a requirement that "the Zip or Postal Code you entered is 5-6 digits long." I live in Australia, and ALL postcodes in Australia are only 4 digits long.

Could anyone provide any help? :P What do I do?