var oldId = "blank";
function swap()
{
                var combo = document.getElementById("combo");
                var id = combo.options[combo.selectedIndex].value;
                var div = document.getElementById(id);
               // Hide old div
                document.getElementById(oldId).style.display = "none";
                oldId = id;
                // Show new div
                div.style.display = "block";
}