Optimum temperature for the fermentation process is about 18-24C for ales and 10C for lagers. Higher than this and it ferments too quickly, this can leave off tasting or "yeasty" flavours in the brew.
In colder climates you can buy special heating elements which keep the brew at the desired temperature.
Bear in mind too, that most of the popular beers in Oz which are marketed as lagers are actually ales and not a true lager (CUB, Tooheys, XXXX). Considering this, you will probably want to brew ales and Sydney would be a great place once the ambient temp is below 24C and you can use a heating element.
