How much is an American 100 dollar bill worth in Australian dollars?

In 2013 the US and Australian dollars were roughly at par, meaning that within a few cents, one USD was worth about the same as one AUD.

As far as specific exchange rates, they change every day so any answer posted here would be out of date almost immediately. While it's not normal WikiAnswers policy to say "use the Internet", that's the best approach in this case. You can check a site such as www.xe.com, CNNMoney, etc. for the latest conversion factors.