Books about computers will become outdated just as fast as the hardware, so the internet is probably your best source for information. Read up, but you might also want to try and get a hold of an old PC you can mess around with, since hands-on learning seems to be the most effective (for me, at least). Sure the hardware might be outdated, but after you take it apart and reassemble it you'll at least have a feel on how everything physically goes together.