You should try professormesser.com he has a 20 - 24 part series of webcasts that show EVERYTHING on the A+ exam. We use it in my computer tech class to learn about hardware and software. Most of it is general knowledge, but there are some points where it gets really specific. I enjoy them, and most of the videos are between 5 and 20 min long. Also, with each there is a PDF file that is basically a list of notes of whats in the movies so you could just read them as well.
On his site he also offers Network+ and Security+ guides.
I myself am also on the same boat. I am a junior in HS, and i take all the computer classes possible, i even go to a vocational course for a period of the day (where i found out about professor messer). Computer literacy is definately a must have nowadays. I just recently got a job as a IT intern with my school district, and to become full time i need the A+ certification. i would take it, I just need a little bit more motivation to study up :P