Cant help but to add to this post.
Australian Aborigines were quite advanced, but since warfare was non existent, they did not evolve techniques for raping the environment as other cultures did. They were here as caretakers and lived without the need to alter the surrounding areas to suit their needs.
They had advanced herb lore for dealing with medical problems like infection and fever. Hunting equipment was quite unique and exceptionally powerful ranging from the boomerang to the Woomera (type of spear launcher .... the similar American version was the atlatl). Regular trade with the islands north, including Indonesia. They had a form of refrigeration for preserving meat.
Lastly, Australian Aborigines have the oldest culture on Earth (est. 50,000+ years), which suggests they found equilibrium with the environment.
Other cultures (i.e. America) are still taking "baby steps"; consider this and they deserve a place in Civ4!
**NOTE: As I understand none of the previous posts were insults to my culture, take this in much the same fashion. When looking at a "Civ", you are viewing its past more than its future or groups like the Mongols or Americans would not have a place in this game.