php and javascript

I have some image urls that I have stored in a mysql database. I want to be able to display the images in a popup window using javascript. But I haven't been able to figure out how to get the get the info to mysql so that the image loads when the popup window appears. Below is an example of the form without any javascript. <form action="test.php" method="post"> <INPUT type="submit" value="See Photo" name="button"> <INPUT type="hidden" name="item_no" value="<?php echo "$item_no"; ?>"> </form><br><br> Any help appreciated. Thanks, SW