Take June 09 exam, meaning you should sign up in Jan, Feb of 09.
Start studying whenever, but be sure to allow yourself enough practice tests so that you can take recent ones in the month before the exam, with the eventual goal of being able to score around your target range consistently. If you can do this, you will have more confidence, and there will be less of a chance of a test day drop.
Powerscore books and your class will be helpful for learning general principles, but you need to take practice tests in order to learn how to apply these principles and handle your timing.