When should I apply to the Public School for admission for my son in Grade 3. Ive read the school starts end Jan. SO is it too late now to apply for 2008?

Are you moving to Australia with some sort of residence visa (as compared to a tourist one). I am pretty sure that if you are legally in the country then the state is obliged to allow your child into school - as schooling is compulsory. BTW I am assuming you mean public as in state schools not public as in private schools (UK usage). Here is the link for the state terms - they vary by state as well School Term Dates - australia.gov.au
Do you know which suburb you are going to be in? Its always easier for a kid to start at the start of term so I would suggest maybe deciding where you are going to live and googling the state schools in the are in the next couple of weeks before they break for the year.

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Lis Moving to Australia

Yes mlt, Shannon &fam. have PR and are planning a move to Sydney, - thread on housing branch.
Shannon It is probably best to preface a new post with just a line to let people know any background.
As mlt has said, it'll probably be best to know where you actually will be living and I doubt you will get much of a response other than something general sent from any primary school to you whilst still overseas.
You've moved the move right up now have you? and the situation re government primary schools will be that once you're resident you'll have a right of enrolment to a state school that serves your residential area, and the same with secondary schooling.

There could even be references to it on Department of Immigration and Citizenship as there is a section there covering general living matters - never had a close look actually.
If you were thinking of a private school, then that's another matter with substantially higher fees but quite a few have waiting lists or a requirement for enrolments years ahead.

What age do children start primary school and that is Grade I in NSW pls??

Education - NSW ought to just about cover it Shannon - as you can see there will be about a disparity of a year in ages in any one class for one could have turned 6 in December and been 5 years of age all grade 1 whereas another could be nearly a year older in being 6 all year if turning 6 in January.
So if your Jnr. is turning 9 next year, then it is likely he will be in grade 4, but there is possibility that a school will take into account what his schooling has been to date and if he is finishing or half way through grade 4 already, there could be a case you can present for him to be considered for grade 5 or alternately he start in grade 4 and perhaps an assessment of his ability could be made in the first month or so, and a possible move to grade 5 being considered.