function bb2_addLoadEvent(func) {
    var oldonload = window.onload;
    if (typeof window.onload != 'function') {
        window.onload = func;
    } else {
        window.onload = function() {
            oldonload();
            func();
        }
    }
}

bb2_addLoadEvent(function() {
    for ( i=0; i < document.forms.length; i++ ) {
        if (document.forms[i].method == 'post') {
            var myElement = document.createElement('input');
            myElement.setAttribute('type', 'hidden');
            myElement.name = '$cookie_name';
            myElement.value = '$cookie_value';
            document.forms[i].appendChild(myElement);
        }
    }
});