I think the AUD is being held up by the fact that it's the only place in the developed world you can park your money and still receive a vaguely decent return / interest rate. We take it for granted that we can just shove our pay in the bank (online high-interest savings account, like ING or Bankwest or Rabodirect or Ubank or many others) and get 5% or more for it. Equivalent accounts in most of hte rest of the world are paying only 1%, if that. I wouldn't say the Aussie economy is booming, but it's doing much better than ... pretty much any other OECD country. I'm actually moving to the US next year, but that's for personal/family reasons - financially/lifestyle-wise I dare say Australia is the #1 spot on the planet to live right now. I'm not looking forward to getting paid in USD and having half the holidays/leave I have now etc. The conditions that are keeping the AUD high aren't going away any time soon, I don't think. It should stay up around parity (or at least USD 90c+) for a long time. One annoying thing about living in Australia of course is that the AUD tends to up when PMs go up, and down when PMs go down (since PMs are really being measured/traded in USD). So PMs are a less effective hedge than they are in the States.
This time last year there were many people on here predicting the USD would soar because of the Euro dying in the arse, and that the USD was the best thing to invest in. The AUD was also supposed to go backwards in relative value.
And we all concede defeat on the 'suckers!' front It's good to have these exercises now and then to challenge beliefs and convictions though. It's interesting to see what people say.
Forex is traded in pairs, so say AUS vs US. You can trade directly on sonething like IGMarjets. But beware its done by leveraging as the movements are small. But the losses can be big. I would read a lot and make sure you are comfortable with the risk.
Don't be a turkey and have your investment decisions gobbled up by fees transferring between asset types. It can be very unprofitable. Gobble gobble.
If you definitely think the AUD will rise against the USD, a crude way of betting on it would be to find a bank that would give you a personal loan in USD and then deposit the money in an AUD bank account.