Marra sent me a post from a national mailing list called Cooeeads, with job postings around the country that are environment-related. Near the top of the list was one for an eco-tour guide working out of Yulara. I note that they provide most of the training, assuming you already have any background in the area. I also note that as with most tour companies they look most favourably on people who already have some sort of 4WD driving/maintenance experience. Maybe you should ask the RACV if they run 4WD courses.