how long in Oz?

Depending on your visa class, (which I won't go into), 6 months would be a good length of time.

12 months would be ideal though.

Aust is so huge.

For a major tourist trip, I think three, maybe four, months is pretty good. This could include a half-circumnavigation: Melbourne (and/or Adelaide), Tasmania, Sydney, Queensland, Alice Springs, Darwin, and fly home or to SE Asia from there (although where you start the loop depends mostly on the month you arrive, to get the best weather). You can easily travel by bus or rail all along the south and east coasts, but I would recommend you fly from Cairns to Alice (say) and Alice to Darwin - these hauls are long and not that interesting for the time they take.<BR><BR>As for visiting Aboriginal communities as a tourist, it isn't always straightforward, however you would probably have the best opportunity in Cairns and Alice Springs, and also Darwin. Communities are not generally open, but quite a few (such as Hermannsburg outside Alice and Nguiu near Darwin) have facilities to accommodate tourists, as do the national parks (interpretive and cultural centres, art galleries, and so on). One way to investigate is to contact the relevant land councils - statutory bodies that represent Indigenous Australians in each region, or the various tourist commissions in each state and territory. Both easy to find on google.

You may be interested to have a look around the website www.greatholidaysaway.com which covers Australia, in particular, very well for... trip planning, things to do and accommodation. Have a great time.

I was there for 2 months, 3 or 4 would have been ideal in my view.

I live in Aust and have to say that for the 23 years I have been alive I still haven't seen all that I want to see. Australia is so massive and diverse that how long you spend here really depends on how long you can afford to spend here.
Central Australia would probably be the most rewarding if you were looking for Aboriginal heritage Uluru (Ayers Rock) would be the ticket, its out of the way but just amazing... I don't think you can climb it anymore but you can get helicopter rides for like $100 for 15mins or so, pricey if your on a budget like most people on lp, me included.
As far as the coast though stick to the north for this part of the year, its winter now in Syd and to cold to swim. Up in Cairns its still good, also over in Broome is nice. Just look up a few places on the net and decide to go from there. But up north on the east you have beaches and the Daintree on the west you got beaches and the Kimberly.
Hope this is a help.
Have a great trip :)