How long you need to study depends on what you already know and how quickly you pick up new information. This will vary by individual. I probably spent about a month on studying for my A+, but at the time had been working in IT for five years. Even with working in IT for five years there were things I still needed to learn, mainly laser printing, something I hadn't had much experience with up until I started studying.
I used the Exam Cram books to study for my exams. They do not walk you through every little thing. They give you the information you need to know to pass the exam. These books are not for people with little or no knowledge on the subject.