function showmenu(elmnt){
            document.getElementById(elmnt).style.display="block";
            document.getElementById("sombra").style.display="block";
            document.getElementById("ctl00_contentorTexto").style.display="none"; 
            document.getElementById("ctl00_tituloPagina").style.display="none";
            document.getElementById("sombratitulo").style.display="none";
            switch(elmnt){
                case "m1":
                    document.getElementById("ctl00_btopo").src="/img/b1.png";
                    break;
                case "m2":
                    document.getElementById("ctl00_btopo").src="/img/b2.png";
                    break;
                case "m3":
                    document.getElementById("ctl00_btopo").src="/img/b3.png";
                    break;
                case "m4":
                    document.getElementById("ctl00_btopo").src="/img/b4.png";
                    break;
                case "m5":
                    document.getElementById("ctl00_btopo").src="/img/b5.png";
                    break;
                case "m6":
                    document.getElementById("ctl00_btopo").src="/img/b6.png";
                    break;
            }
           }
        function hidemenu(elmnt){
        document.getElementById(elmnt).style.display="none";
        document.getElementById("sombra").style.display="block";
        document.getElementById("ctl00_contentorTexto").style.display="block"; 
        document.getElementById("ctl00_tituloPagina").style.display="none";
        document.getElementById("sombratitulo").style.display="block";
        document.getElementById("ctl00_btopo").src= document.getElementById("ctl00_bTopoa").src;
        }

 if (document.images)
    {
	
      preload_image_object = new Image();
      // set image url
      image_url = new Array();
      image_url[0] = "http://www.prosonic.pt/img/fmenu.png";
      image_url[1] = "http://www.prosonic.pt/img/sombra.jpg";
      image_url[2] = "http://www.prosonic.pt/img/fsite.jpg";
      image_url[3] = "http://www.prosonic.pt/img/imgTopo1.jpg";
      image_url[4] = "http://www.prosonic.pt/img/fConteudo.png";
      image_url[5] = "http://www.prosonic.pt/img/cConteudo.png";
      image_url[6] = "http://www.prosonic.pt/img/linkR.gif";
      image_url[7] = "http://www.prosonic.pt/img/sombra.jpg";
       
       var i = 0;
       for(i=0; i<=7; i++) 
         preload_image_object.src = image_url[i];
    }