baggins,
you can trade CFD's through comsec.
http://www.comsec.com.au/Public_FrameSet.asp?Page=HProducts
Here is a broker which might be of interest for short selling.
http://www.traderdealer.com.au/short-selling.aspx
Here is some general info.
Good Luck!
http://www.bwts.com.au/index.cfm/resources/ask-colin/569-why-is-it-not-possible-to-sell-short-on-the-australian-stock-mar/