Many people take courses, usually the Kaplan course. I didn't. If you want to and you have $1500 burning a hole in your pocket, go for it. It's certainly not a requirement.
Any of the review materials will cover the basics--I used First Aid and Step Up for both the exams, and I also liked "Step One Made Ridiculously Simple" but I didn't buy the Step Two version. I also highly recommend getting hold of a set of Dr. Goljian's lectures on CD--I had them on my iPod and they were incredibly helpful. (PM me if you can't find what I mean--they are usually readily available for download online somewhere.)
I echo your other online friends' advice that the most important thing to do is to do lots of practice questions, and to time yourself. It has been my experience as both a student taking the exam and a tutor that the biggest problem people have with the exam is the time constraints. If you go to the USMLE site, you can download all the rules about how the test will go, but basically, you will be doing one-hour blocks with 50 questions each, and you will be allowed certain amounts of break time throughout the day--but once you start any given block, you have to finish it in that hour. So the test does require a certain amount of stamina, and you have to be able to read the questions quickly and accurately.
There are a number of places that offer a question bank online (including Kaplan, who probably has the best-known, and USMLE World, who my school subscribed to as well) and whether or not you are taking a course, it is probably well worth the money to purchase access to one of them. Doing lots of questions online and doing them in a similar format to what the test will be like is probably the best preparation you can have, and it will also help you identify any areas of weakness that you need to review.
Good luck! The tests are long and the material is extensive--they can basically ask you anything they want about anything you should have learned!--but it is do-able.
Fourth year medical student. Next up, Step Three after internship year! It never ends!