I wouldn't touch them with a barge pole. Go to someone who knows what they are doing, like Energy Matters (I just had an EM solar system installed on the weekend) or a reputable company like Solargain, Eco Kinetics, Energy Aware, Ingenero, Enviromate and so on.
Avoid Modern Solar, I have read horror stories about them.
Get at least three quotes. You can get quotes here:
http://www.solarquotes.com.au/
Also, do some research on whirlpool.net.au, the Home forum.
