Rollover "GO" image for search form not changing

[Jirbytaylor]

I am working on a Wordpress blog, and have been so far customising a theme to my liking, however the search button has got me stuck.

[spoiler]

Code: [Select]

      <form method="get" id="searchform" action="<?php bloginfo('url'); ?>/">
        <input type="text" value="<?php the_search_query(); ?>" name="s" id="s" /><input type="image" id="search_submit" src="<?php bloginfo('stylesheet_directory'); ?>/images/go.png" onmouseover="<?php bloginfo('stylesheet_directory'); ?>/images/go_hover.png" onmouseout="<?php bloginfo('stylesheet_directory'); ?>/images/go.png" value="Search" />
      </form>[/spoiler]
This is the searchform.php file, as you can see there are onmouseover entries yet they don't seem to work. The image does not change. My suspicion is that it may be to do with the face the image isn't a real image - not using an img tag - but a form button?

This is my blog here to see the search form itself:
http://jirby.cleverpun.com/blog/

Thanks in advance for any help.