Hi lubby - sorry we missed this thread.
Yes, you are entitled to your old job, as long as it still exists. If it no longer does, then you are entitled to a comparable position.
Go to the office of industrial relations website: work and family dot nsw dot gov dot au (sorry, I don't think I'm allowed to post the link. Ignore the spaces.) and check out the maternity leave section under 'employer responsibities'.