<!--[if lt IE 7]>
 function alphaBackgrounds(){
   var rslt = navigator.appVersion.match(/MSIE (\d+\.\d+)/, '');
   var itsAllGood = (rslt != null && Number(rslt[1]) >= 5.5 && Number(rslt[1]) < 7.0);
   for (i=0; i<document.all.length; i++){
     var bg = document.all[i].currentStyle.backgroundImage;
     if (itsAllGood && bg){
       if (bg.match(/\.png/i) != null){
         var mypng = bg.substring(5,bg.length-2);

         //if (mypng.substring(mypng.length-16, mypng.length) != "top_nav_left.png" && mypng.substring(mypng.length-17, mypng.length) != "top_nav_right.png") {
         	document.all[i].style.filter = "progid:DXImageTransform.Microsoft.AlphaImageLoader(src='"+mypng+"', sizingMethod='scale')";
         	document.all[i].style.backgroundImage = "URL('../images/x.gif')";
         //}	
       }
     }
   }
}

window.attachEvent("onload", alphaBackgrounds);
<![endif]-->