best reference to theming I'm completely new to drupal and am starting to take interest in the process of theming. I was wondering if anyone could suggest a reference or perhaps even just insert a snippet of code explaining the basic template.

I have some PHP experience but nothing too complex. I'd really like to learn how to apply javascript into my themes and what the best approaches would in terms of that. I attempted the other day to insert some HTML via the regular "create content" section and then wrote a stylesheet to correspond to said HTML, I linked via the template.info file, but it didn't work because Drupal had renamed all of my div's. Is that normal?

Sorry if my question seems to be too broad in scope, I guess I just need a direction or map and I'd be fine. Thanks in advance, and looking forward to becoming a contributing member of this community.
I recommend the theming chapter by @jacine in Definitive Guide to Drupal 7 - http://definitivedrupal.org/. Not free but well worth it.