I'd just like to add that the SAT is nowhere near as intense as the VCE. The SAT Reasoning Test is done in a single sitting, and is made up entirely of multiple choice questions. Whereas no one would ever think of sitting a VCE exam without prior preparation, it is very possible to take the SAT and do well in it without much targeted study. From memory, the SAT Reasoning Test is divided into 10 sections; there are a couple of sections on critical reading, a couple on mathematics, and a couple on writing. The maths sections are really straightforward; most of the questions are at year 9-10 level. The critical reading and writing sections are substantially harder, although still manageable for those who have a large vocabulary. In many respects, the SAT Reasoning Test is like the GAT; it tests general skills, and is a test that you cannot really study for (although I've heard stories of some American children beginning their preparations for the SAT from year 7...:/).
On top of the SAT Reasoning Test, you will also have to complete 2 to 3 SAT Subject Tests, as MrsStark alluded to above. It is largely up to you what subject tests you want to take. If you are looking to study mathematical sciences in the US, then it might be wise to do subject tests in, say, maths and physics, or maths and chemistry. If you are looking study humanities, then it might be more rational to do subject tests in, say, literature and history. Again, these tests consist mainly of multiple choice questions. However, unlike the SAT Reasoning Test, you will need to do at least some preparation for the SAT Subject Tests, as they test really specific knowledge. That said, the SAT Subject Tests are nowhere near as hard as their VCE counterparts. The SAT Subject Test in Chemistry, for example, tests mainly Unit 1 & 2 stuff, and so studying for the corresponding VCE subject is more than enough preparation.
As you've probably figured out already, if you are looking to study overseas in the US, you'll have to complete a separate application. This application is called the Common Application, and the SAT forms but a part of it. In addition to the SAT, you will also have to obtain 2 recommendation letters from 2 different teachers. I've been told that more emphasis is placed on recommendation letters than SAT scores. It is possible for a student with perfect SAT scores to be rejected due to weak recommendation letters. The important thing to bear in mind is that US unis are not only looking for students who excel academically, but students who have taken the initiative to do something meaningful with their lives.
Best of luck, AceVCE777! It's great that you are thinking ahead!
