My IE 7 doesn't seem to support PNGs like yours does.

How about in the head:

<!--[if lt IE 7.0000]>
   <script type="text/javascript" src="/jquery/plugins/
jquery.ifixpng.js"></script>
<![endif]-->
<!--[if gte IE 7.0000]>
   <script defer type="text/javascript" src="/javascript/pngfix.js"></
script>
<![endif]-->

And and then in
$(function(){

  //Use jQuery plugin to fix PNG images in IE 6
  if( $.browser.msie && (jQuery.browser.version < 7.0000) ) {
    $('img[@src$=.png]').ifixpng();
  }

}