function tertiary_nav_hover(){
        var atags=document.getElementById('nav1').getElementsByTagName("a");
        for (var t=0; t<atags.length; t++){
        	imgtags=atags[t].getElementsByTagName("img");
        	imgtags[0].onmouseover=function(){
        		var img_src=this.src
        		img_src=img_src.replace(".gif","_on.gif"); 
        		this.src=img_src;
        		}
        	        		
    
  		 imgtags[0].onmouseout=function(){
  			var img_src=this.src
       		img_src=img_src.replace("_on.gif",".gif"); 
       		this.src=img_src;
    	}
	}
}
    

if (window.addEventListener)
window.addEventListener("load", tertiary_nav_hover, false)
else if (window.attachEvent)
window.attachEvent("onload", tertiary_nav_hover)