I use this circuit simulator occasionally.  It's not the most accurate, but it does teach me a thing of two.

Have you ever wanted to create your own PC board?  I saw this site recently and plan to try it out.


It looks as if they require Gerbel files.  I found that, as a hobbyist, you can download a "limited use" version of Autodesk Eagle for free.  I still need to learn how to use it.