<script type="text/javascript">
var is_countdown_started = false;
var text = '';
function countdown_new(_el, _sec) {
   var el = document.getElementById(_el);
   if (!el) {
   return(false);
   }
   if (_sec > 0) {
   if (!is_countdown_started) {
   text = el.value;
   is_countdown_started = true;
   el.disabled = true;
   }
   el.value = 'Прочитал и соглашаюсь (' + _sec + ' с.)';
   setTimeout('countdown_new(\'' + _el + '\', ' + (_sec - 1) + ')', 1000);
   } else {
   is_countdown_started = false;
   el.value = text;
   el.disabled = false;
   }
}
window.onload = function() {
   countdown_new('button1', 30);
}
</script>