Working holiday visas valid for 12 months are available for those aged between 18 and 30. Annual allocation starts in July. Once these run out, you will have to apply in the following year. 78,000 of the visas were issued in the year 2000. Your main reason for visiting Australia should be a holiday, with work being used to supplement your funds.
Permanent migration is on a points system and more difficult to obtain.
It helps if you have a skill that's in short supply or family living in the country. One of the biggest sources of seasonal employment is fruit picking but there are also short term jobs in offices, finance, nursing, telemarketing hospitality and au pair work. TNT Magazine, a free publication for travellers with job listings is widely available at hostels, travel centres, train stations and airports. Their excellent website has a harvest calendar, classified ads and advice for working travellers in Australia. Employment National, the privatised government employment service, has a section on seasonal fruit picking vacancies.