DVDdoug:
Does [u]this[/u] help?How much electronics do you know? Before you try to understand transistors, you need to at least know [u]Ohm's Law[/u] and [Kirchhoff's Laws](http://Kirchhoff's circuit laws).
If you were studying electronics in school, you'd have a semester of DC curcuits, and a semester AC circuits before you start learning about transistors, MOSFETs or other active devices.
That is big factor/problem in lots of new users and their approach to electronics as they start to design and build their arduino projects. I can't blame them for wanting a head-start/leap-ahead approach to electronics much as the Arduino programming language has lots of aids to simplify the programming side. However they will always pay for their lack of ability to figure out/troubleshoot their own circuit designs. So we just keep having to ask them to post their schematic drawings and look for their fundamental mistakes. It's why we make the big bucks around here. 
Lefty