<html>
<head>
<script type="text/javascript" language="javascript">
function go(sec) {
var btn = document.getElementById('btn');
btn.value = sec;
if (sec > 0)
setTimeout(function(){sec--;go(sec);}, 1000);
else {
btn.value = 'Отправить';
btn.disabled = '';
}
}
</script>
</head>
<body onload="go(10);">
<input type="submit" disabled="disabled" id="btn" />
</body>
</html>