Well, I had always liked computers since I was very little...when my dad got an IBM PS/2 Model 30 286. After that, we got a 486 with Windows 3.11 and then a PII 333. I spent a lot of time on both of those machines, and especially got to know how to do troubleshooting in Windows. I also read a lot of stuff on the web, at Sharky Extreme mainly. Then I started doing upgrades on my own, and not too long after that built my first PC. I have done 3 all together now, and have learned a lot from doing each one. I am only a sophomore in HS, so I have a long way to go in learning things. I hope to take it to a formal level, taking computer science in college and getting a job in the industry.
To sum it up, I obtained most of my knowledge from the web (especially forums) and from personal experience.
EDIT- Can't believe I forgot to mention TechTV (formerly ZDTV). I watched them religiously for a long time, and learned a great deal from them, especially on Call for Help and The Screen Savers.