Drupal resources (the short list) http://drupal.org/start http://acquia.com/resources http://www.lullabot.com/ http://www.lynda.com/search?q=drupal
Do you want to focus on developing or theming? I recommend you pick one to start at least. It's taken me many years to be able to do both.
For front end theming you need to know CSS and jQuery, and a bit of PHP and HTML.
For back end developing you need to know PHP and MySQL and HTML, and a bit of CSS and jQuery.
Some people think theming is easier but I know from experience they both are complex in different ways.
Good tutorials for HTML CSS JavaScript jQuery PHP MySQL and more at http://w3schools.com
Also, I think you should just focus on learning Drupal 7. By the time you are ready, D6 will just be used on legacy sites.
