Justin Silverton shows how to create an Upload Progress meter using PHP 5.2 and Yahoo User Interface. Prior to PHP 5.2, there’s no way a PHP script could monitor the progress of a file upload, causing programmers to look at Perl scripts to provide the same information. For a demo, head over to http://progphp.com/progress.php
This progess meter is based on the yahoo user interface library and alternative php cache (APC). You will need both of these for it to display properly. PHP 5.2.0 or higher is also required. (I have written a previous article on alternative PHP cache here). 

Jaslabs: High performance php » How to create a php upload progress meter