function available() {
    if (!document.getElementById) return false;
    var ftable = document.getElementById("flat_table");
    var td = ftable.getElementsByTagName("td");
    for (var i=0; i<td.length; i++) {
        if (td[i].className == "available") {
            td[i].onmouseover = function() {
                this.className = "availhover";
            }
            td[i].onmouseout = function() {
                this.className = "available";
            }
        }
    }
}

addLoadEvent(available);