function showdiv(whichDiv) {
    /* make all the unhidden classes hidden */
    setClassByClass('unhidden', 'hidden');

    if (whichDiv != '') {
        /* make the specified class unhidden */
        setClassById(whichDiv, 'unhidden');
    }
}

function setClassById(id, c) {
    var div;
    div = document.getElementById(id);
    div.className = c;
}

function setClassByClass(searchclass, setclass) {
    var divs = getElementsByClassName(searchclass)

    for (i = 0; i < divs.length; i++) {
        divs[i].className = setclass;
    }
}

function getElementsByClassName(c) {
    var my_array = document.getElementsByTagName("*");
    var retvalue = new Array();
    var i;
    var j;

    for (i = 0, j = 0; i < my_array.length; i++) {
        if (my_array[i].className == c) {
            retvalue[j++] = my_array[i];
        }
    }
    return retvalue;
}