Hello,
having the same Problem yesterday when I try to load the Scripts in a Theme Header.
Loading the Scripts by this way for Admin Functions works fine.
Now I have a Solution for the Frontend:
wp_enqueue_script('theme_js', get_template_directory_uri().'/js/theme.js', array('jquery', 'jquery-ui-tabs'));
The third parameter ($deps) is crucial.
After this call the Scripts jquery.js, ui.core.js and ui.tags.js were loaded in the Theme Header. (Tested in WP 3.0)
From Doku:
$deps (array) (optional) Array of handles of any script that this script depends on; scripts that must be loaded before this script. false if there are no dependencies. This parameter is only required when WordPress does not already know about this script.
Hope it will help you to.
Sabine
P.S.: Sorry for my bad english ??