function showMenu (act, menuId)
{
    var cssElement = document.getElementById(menuId);
    var elementStyle = cssElement.style;

    if ( act == "~" )
        act = (elementStyle.visibility == "visible") ? (0) : (1);

    if (menuId.split("_", 1) == "sub") {
        var imgElement  = document.getElementById("arrow_" + menuId.split("_", 2)[1]);

        if ( imgElement )
           imgElement.src = ( act == 1 ) ? "img/expanded.png" : "img/collapsed.png";
    }    

    if ( act == 1 ) {
        elementStyle.visibility = "visible";
        elementStyle.display = "block";
    } else {
        elementStyle.visibility = "hidden";
        elementStyle.display = "none";
    }
}