Cannot get JQuery plugin working on Drupal 7
From the Drupal 7 upgrade guide:


  Javascript should be made compatible with other libraries than jQuery
  by adding a small wrapper around your existing code:


(function ($) {   
      // Original JavaScript code. 
})(jQuery);



  The $ global will no longer refer to the jquery object. However, with
  this construction, the local variable $ will refer to jquery, allowing
  your code to access jQuery through $ anyway, while the code will not
  conflict with other libraries that use the $ global.


(function ($) {
  // Create the tooltips only on document load
  $(document).ready(function() {
    // By suppling no content attribute, the library uses each elements title attribute by default
    $('#content a[href]').qtip({
      // Simply use an HTML img tag within the HTML string
      content: 'dfdfdfdfdf'
    });
  });
})(jQuery);