Hi, I also want to be a vet :) (I'm in grade 12 this year)
I'm in QLD too. Only year 12 counts. If you miss a big chunk of yr 12 then they consider your year 11 marks. To get into vet straight from school you need an OP 2 for Queensland University, I think James Cook is a 3. OP 2 is a very high mark, depending on your school this is about the top 10 students or so. However, even if you don't get the mark, you can do a uni course for one year and if you do well then you can tranfer into the vet course.
Hope that helps