Is science teaching in Australia (Sydney) a good job? Are the schools ok? Are the kids well behaved?

I know that the education system is different as i am from dreary old ireland! Is there much demand for teachers? Thanks.

It depends on where exactly in Sydney you want to teach. There is a need for Science and Maths teachers in public secondary schools - but any other teachers in the public schools (particuarly primary) - you'll be on a waiting list....
Much easier to find a job in private education - look on the Sydney Morning Herald newspaper/jobs section to see ads. You can also approach private schools yourself with your CV and relevant qualification - and you might get casual work which could well lead to full time. If you are willing to go somewhere further from the city, or on the outskirts of Sydney, you'll have more opportunity as the demand for teachers is greater. The behaviour of the kids varies from school to school. Not as bad as the kids in London, but not as good as the kids in Japan ;) I don't think you can generalise a whole city's kid's behaviour.
The schools vary wildy suburb to suburb as well, for example the schools in Sydney's eastern suburbs like Bondi and Double Bay are largely private and very expensive. In less 'prime real estate' areas like Mt Druitt, the schools are known to be 'rougher'.
As far as being a 'good' job - do you mean pay wise? It's fine - depending on how many years experience you have, but even first year's pay isn't dire. Enjoy.

a huge demand for teachers over here!!!
casual and full time. espacially in smaller communities.
ive just started my first year at uni to become a science teacher actually :)

well i'm an australian kid
and i think the discipline of kids in australia isnt that good
the generation of people who are lik 12 to 33 years old are called generation y
we're supposed to be disrespectful and aren't happy with what we get

but we're not that bad lol
public educatin is also pretty good
but the demand for private education is growing

there is a huge demand for teachers
but teachers in victoria are being paid the least and are constantly on strike
so dont come to victoria

Most schools are ok, you are never going to get the perfect class but most are good.

Some schools however, have a reputation the preceeds them...Try to avoid those schools.

I'm pretty sure we are pretty teacher-lacked at the moment.

But don't take my word for it, come over and see for yourself.
:)