Hi Huy,
function countdown()
{
now = new Date();
urlaub = new Date(Jahr, Monat, Tag, Stunden, Minuten, Sekunden); //monat: januar=0, dezember=11!
diff = urlaub - now;
diff_m = Math.floor(diff / 60);
diff_s = diff % 60;
document.countdown.countdown.value = diff_m + ':' + diff_s;
}
<body onload="countdown(); setInterval('countdown()', 1000)">
<form name="countdown">Noch <input type="text" name="countdown"> bis zum urlaub!</form>
Gruß, Marian