<script language="javascript">
  function $Do(str,form)
  {
     switch(str){
        case "OK":
          form.action="a.asp"
          str="OK1";
          break;
        case "OK1":
          form.action="b.asp"
          str="OK2";
          break;
        case "OK2":
          form.action="c.asp"
          break;
        default{}
     }
  }
</script>
<form onsubmit="$Do(this.submit.value,this)" target="_blank">
 <input type="submit" name="submit" id="submit" value="OK">
</form>