The Australian Greens are now the third largest political party in Australia. In the 2004 Federal election, we find the following results (primary votes for House of Representatives):
Liberal Party of Australia: 40.81% of the vote
Australian Labor Party: 37.64%
Australian Greens: 7.19%
National Party of Australia: 5.89%
Family First: 2.01%
A more recent election was the 2006 Victorian State election. Again we find the following results:
Australian Labor Party: 43.06% of the vote
Liberal Party of Australia: 34.44%
Australian Greens: 10.04%
National Party of Australia: 5.17%
Family First: 4.29%
If you go back and look at the electoral history since the Greens were first founded in 1992, you'll notice that their popularity has increased markedly over that time. At one point in history, the Australian Democrats were considered Australia's third party, but their popularity has decreased markedly since their leadership problems in the least 5-10 years. In fact there is a direct correlation between the rise of the Greens and the demise of the Democrats.
The difference between the two parties (apart from ideology - the Greens are from the left side of the spectrum while the Democrats are from the centre) is that the Democrats have never reached such heights of voter support. As you can see from the 2006 Victorian state election, the Greens have 10% of the vote these days.
There's no way in the world that the Greens will win a lower house seat in the upcoming NSW State election. Polls have the Greens at 6% of the primary vote but I suspect the number will be higher. I predict the Greens to crack at least 8% of the vote in NSW. Why? Al Gore.