Can I use my IPad 3G in Australia which has 230v?

Yes. The power brick for the iPad can handle input voltages between 110 and 240 volts.

The iPad 3, like all USB charged devices requires 5 volts DC. The Apple supplied charger can be used with AC input voltages from 100-240volts AC @ 50-60 hZ. It will output 5 Volts DC, no matter the input.

As noted by the others yes...

You may need to purchase an adapter for the wall outlet before yup go or after you arrive in Oz...

http://www.worldstandards.eu/electricity/plugs-and-sockets/

http://www.kropla.com/electric2.htm

You can pay huge prices, including to Apple, but the cheapest plug adapter I found during our Oz adventure was in the AA store - the motoring one, not the alcoholics.