Eck, now that I've withdrawn from Int St all the questions roll in!
Ok, well, how much Japanese you learn is entirely dependent on which level you commence. If you start your four semesters of Language and Culture at level 1 (ie no prior study of Japanese) then you will learn a lot of basic Japanese, by the end of which you should be able to survive in Japan. If you studied to HSC Continuers level you will commence at level 3 (assuming you forget as much as everyone else) and will be a bit better off, with the ability to make some conversation. HSC Extension people will (if they keep their Japanese up during the year) commence at level 5, and finish at level 8 (the highest offered). This level of Japanese is sufficient for more complicated conversation.
Judging by the kanji lists I had to study (I didn't know I got medicine until much later than everyone else) you do learn quite a bit of Japanese, a lot more than you would study in the same time at school. Of course, that's the case for anything at university.
The year in Japan will be a year of total immersion, and I expect it would essentially double your proficiency (depending on how good you are when you arrive). The less you know when you get there, the more marked the difference will be when you leave. However, if you turn up having completed level 5 you will be able to expand on your specialised vocabulary a lot better, and after your year in Australia should be a lot more impressive in the eyes of prospective Japanese employers. I was intending to apply to major research and production companies in the electronics field, such as Sony, Canon, Toshiba etc.
Assuming you complete all prerequisites, all International Studies students go for ICS in their fourth of five years. For me this would have been 2007, and I was planning on living in Yamanashi.