Absolutely. I think multi-alphabetic support is better handled in OS X than in Windows. There’s even an option for Greek with breathings and accents, which is what I’ve needed when putting quotations in Ancient Greek in (you need extra software to achieve this in Windows).
When you get your Mac, go to System Preferences > International, then choose the 'Input Menu' tab. Make sure that there is a tick next to 'Keyboard Viewer', and then also tick all the languages whose keyboard layouts you want to access—in your instance you’d want Australian and Greek at least. Also make sure that 'Show input menu in menu bar' is ticked at the bottom of the Preferences window. You can also access the settings to change the keystroke shortcut for changing the input source language/layout from there.
Then a flag will appear in your menu bar—Australian by default (because you'll be set on the Australian keyboard layout). You can then change the keyboard layout by clicking on that flag and choosing the layout you want (Greek), or by using the keyboard shortcut to switch input layouts (so the flag will change to a Greek flag). Also from that menu you can choose the Keyboard Viewer: this is very helpful when you're typing in an alphabet whose keyboard you haven't got, so you can see which characters map onto which keys on your own keyboard.
