For recent mysql versions you'd better use mysqli instead of mysql. It's much faster. It is especially critical when you are debugging it (e.g. with Eclipse, see http://www.zend.com/pdt ). So if you just "blindly" followed this walkthrough, like me it applies also to you.
You'll have to add the line
or similar to your php.ini (e.g. C:\PHP\php.ini), and restart Apache.
Then you can debug Drupal as "PHP web page" from Eclipse.