Hi frankdogg
All you really need to get a taste of tri is a bike and some running shoes. That's it! Don't worry if it's a mountain bike - you won't want to splash out on an expensive roadie if you don't like the sport.
You will get the same feel for the multi sort aspect of tri if you jump off your mountain bike after a ride and the run straightaway. Lots of people do their first race on a moumtain bike, anyway.
You don't say what State you are in, but if you visit the Triathlon Australia website here -
http://www.triathlon.org.au/ you can find your Sate Association website under the "Community" drop-down. The Rules are there under the "Officiating" menu.
Once there, it's easy to find a list of affiliated Clubs in your area/suburb/town. It's nearly the end of the season, but many clubs run winetr duathlons or runs, so rock up anyway and make some new friends, get some advice. Triathletes LOVE to give advice to noobs (check me out!).
Good luck with it, it's a great sport, and remember - you can spend a lot of money if you want to, or next to nothing. It's all about taking part.
Cheers