<form method="get" id="f1" action="http://www.yandex.ru/yandsearch" onsubmit="return FoprmSubmit()">
       <input type="text" name="text" /> <input id="SubmitButton" type="submit" value="Отправить" />
    </form>
    <script language="javascript" type="text/javascript">
    function FoprmSubmit()
    {
       f1.submit();
       document.getElementById("SubmitButton").disabled = true;
        return false;
    }
    </script>