If you were a member of Anticipation, last year's Montreal worldcon, you can nominate without being a member of Aussiecon 4. Of course, all members of Aussiecon 4 can nominate as well.
I know I sound like a broken record about this, since I say the same thing every year... but nominating is the most important part of the whole process, IMNSHO. Lots of people vote every year, choosing one of the five finalists in each category, but only a comparative handful bother to nominate and determine who gets on that final ballot. It IS an honor just to be nominated -- and can be a career boost as well, especially for a new writer. If you look at the results released each year after the Hugos, you'll see that in many many cases a single nomination makes the difference between who makes the cut and who doesn't.
So NOMINATE, folks. If you don't, don't complain to me about the final ballot.
As to what you should nominate... well, that's up to you, of course.
In past years I've done a whole series of posts about books, stories, writers, and artists who I thought who were worthy of nomination. This year I don't have the time... and anyway, those postings never seemed to have much effect. So let me just say that I still think Michael Komarck deserves a place on the Best Professional Artist list, that Ian Tregillis would make a terrific nominee for the Campbell Award, that Daniel Abraham's THE PRICE OF SPRING was surely one of last year;s best novels, and that all the stories in SONGS OF THE DYING EARTH are eligible in their respective categories (short story, novelette, novella), and that THIS IS ME, JACK VANCE! should be considered for Best Related Book.
I liked WATCHMEN too, and hope it makes the list in Best Dramatic Presentation, Long Form, although I fear that nothing will withstand the AVATAR juggernaut.
Now go ye forth and nominate. The clock is ticking.