Using CDN for jQuery and jQuery-ui with Drupal 6
Those files look to be available https://ajax.googleapis.com/ajax/libs/jqueryui/1.8.14/jquery-ui.min.js

update

As to why it didn't work:


Jquery that ships with drupal 6 is 1.2.3
The Jquery update module can push this to 1.3.2


You are trying to use a much more recent version of jquery than Drupal 6 can handle. Drupal uses a lot of jQuery in it's workings, so it is not straightforward to put a new version on top. Sorry I didn't spot that earlier.