function setOpacity(el, n) {
 //n can go from 0 to 100;
 if(n == null) n = 100;
 el.style.opacity = n/100;                   
 el.style.filter  = "alpha(opacity='" + n + "')";
}

function showDiv(id){
    document.getElementById(id).style.display = "block";
    setOpacity(document.getElementById("layout"),30);
}

function hideDiv(id){
    document.getElementById(id).style.display = "none";
    setOpacity(document.getElementById("layout"),100);
}