I'm going to Australia for both business and pleasure for two weeks. Do I need a special visa for this?
The relevant visa for this case seems to be ETA (Business Entrant - Short Validity) subclass 977. Since you mentioned you're going for a conference, a longer validity business visa should not be required. It can be applied for online.
Visitor/tourist visas will probably not fit as only 'limited volunteer work' is allowed under them.