function Mouse_over(obj)
{
    a = document.getElementById(obj);
    if (a!=null)
        a.src = a.src.replace("on.gif", "off.gif");
}
function Mouse_out(obj)
{
    a = document.getElementById(obj);
    if (a!=null)
        a.src = a.src.replace("off.gif", "on.gif");
}