I have been taking an LSAT prep course class since May in preparation for the October test. I went through Princeton Review, and I have loved it. If I had just got some books, I don't think I would have any clue how to properly solve some of the questions. What you should do is go on the Priceton Review website and take a practice LSAT. If your score is below a 155, you should probably take a class. If it is above that, you can probably just practice using a book or online program and improve your score that way. I think 5 months is adequate time to prepare. The more you practice LSAT questions, the better you will do.
You also need to go to
Law School Admissions Council website. This will give you info on how to sign up for the LSAT, tell you about registering with the Law School Data Assembly Service (which you must register with before applying to any schools), and give you all sorts of other helpful hints about law school.
I know what you're going through! I'm stressing about the October test as well, and right after that I have to start doing applications! Good luck, if you need anything else you can PM me!
~Shae