The HSC Latin course is called a 'Continuers" course, ie. it is for people who have done Latin through Stage 5 ie. (years 7-10). I'm fairly certain no Latin Beginners Course exists which is like Japanese beginners course. If you haven't done it before, I'm not sure you can, although i might be wrong.
latin is the best subject though! (I am biased) I think it's a combination of both the study of the language and of the writing style. In the first few years you learn basic grammar and structures, and by the prelim and HSC course you're able to appreciate the subject in context, and that's when you start studying the works of Roman authors and poets. its as much a study of the language as it is of culture and history.
plus it helps you with English, and you devlop a certain fondness for it which makes you seriously consider it for university.
do it if you can!
Weisy