<SCRIPT language=javascript>
  function CheckPost()
  {
    if (myform.user.value==""}
    {
      alert("please input user name!");
      myform.user.focus();
      return false;
    }
    if (myform.title.value.length<5)
    {
      alert("Title length can't less 5 chars");
      myform.title.focus();
      return false;
    }
  }
</SCRIPT>

  <form action="add.php" method="POST" name="myform" onsubmit="return CheckPost();">
    User    :<input type="text" size=10 name="user"/><br>
    Title   :<input type="text" size=20 name="title"/><br>
    Content :<TextArea name="content" rows=10 ></TextArea><br>
    <input type="submit" name="submit" value="Send Message"/>
  </form>