Short selling is available through some brokers and only for limited stocks. Generally the easiest method to get short exposure is via CFD provider though - although these will over have a further limited short book.
A quick check of AHZ short positions (http://www.shortman.com.au/stock?q=ahz) shows basically none. Usually posters screaming shorts are killing their stock is because they can't deal with the fact that its heading down and no-one wants to buy it for the price they want.. in some cases though, the volume of shorts against a stock can have an impact - even if just sentiment and physcological.
This one is longer, but probably explains it a bit better:
