Being in Australia, you have different 'rules' and laws than many of the responders from other parts of the world. Use the search function to help find the proper answers.
As for using a credit card online, believe me when I say that so far there have been no fraud cases involving poker sites THAT HAVE SURFACED. Depending on what browser you use, always look for a security lock icon somewhere on your screen when asked for a Credit Card #. That indicates the window and its contents are secured, and scrambled in some way to prevent the info from going anywhere other than intended. So in general, most credit card transactions are safe. If you can not find a LOCK ICON do not press enter to send that info!