[Mooff]

two possibilities come to mind:
a) you do not have the jquery1.4.4.js file in the vbulletin folder
This would mean search

 <script type="text/javascript" src="clientscript/jquery/jquery-1.4.4.min.js"></script>

and replace with

 <script type="text/javascript" src="' .$slider_img_filepath. 'jquery-1.6.1.min.js"></script>

b) you already have a jquery version running on the page where the slider is included.
Just delete that line. Two jquery files on one page are unnecessary and unfortunately break the jquery execution.

 <script type="text/javascript" src="clientscript/jquery/jquery-1.4.4.min.js"></script>

If the jquery version you are using on your website is above 1.4 - you are fine and everything should be working now.
If it isn't - update your version.