Not to be cheeky but if you're familiar with programming and JavaScript I'd start with the jQuery source:

http://ajax.googleapis.com/ajax/libs/jquery/1.3.2/jquery.js

Be patient and focus on understanding one part that your are familiar with - perhaps handling AJAX requests.

You need a little more than familiarity with programming to get started with a JS toolkit.

Most JS toolkits are heavily biased towards the browser environment, so you also need some knowledge of the DOM and the host environment provided by browsers for JS execution.

That said, if you feel like experimenting, I'd recommend using Firefox, installing FireBug and reading http://docs.jquery.com/Tutorials:Getting_Started_with_jQuery . That should get you started.