Hi there,
Each state/territory is different from the others in lots of different ways (weather/population/landscape)

Just a quick run down (Im sure others will add to the list)

Australian Capital Territory (ACT)- Canberra
* is very picturesque
gets warm in summer, and very cold in winter

Queensland-Brisbane
* The further north you go, the warmer it is (ex: Cairns is warm all year, 6 months warm, humid, wet and the other 6 months warm and dry)
* further south it gets very warm in summer, and winters are still generally mild

New South Wales-Sydney
* can be warm in summer, and does get cool in the winter -more so in the mountainous regions
* further nth you go in NSW, the warmer it gets

Northern Territory-Darwin
* is generally warm all year
again hot, humid, wet for 6 months, hot and dry the other 6 months

South Australia-Adelaide
* has very warm summers and winters can get cool-especially in the SE areas.

Tasmania-Hobart
* is the coolest of the states
summer is mild, and winters are very cold

Victoria-Melbourne
* can have warm summers, and cold winters
also known as the state that can have all 4 seasons in 1 day
(personally my fav area of all)

Western Australia-Perth
* summers can be hot-especially nth of Perth and winters can ce cool-cold in southern areas

Hope this helps...they are all very different places