We have seen checking username availability using jQuery in earlier post. Here is a slight modification on showing of error/success message. The message will be shown as popup and disappears after few seconds. Using this way we can show the message in more fancy way.
The Javascript Code:

<script src="http://ajax.googleapis.com/ajax/libs/jquery/1.4.2/jquery.min.js" type="text/javascript"></script>
<script type="text/javascript">
function checkUserName(usercheck)
{
	var uname = document.getElementById('username').value;
	$.post("checkuser.php", {user_name: uname} , function(data)
		{
			   if (data != '' || data != undefined || data != null)
			   {
				  $('#usercheck').show();
				  $('#usercheck').html(data);
				  setTimeout("$('#usercheck').hide(); ", 3000); //display message for 3 seconds
			   }
          });
}
function checkUserLogin(user_id)
{
   if (user_id == '' || user_id == undefined || user_id == null)
   {
	  $('#logincheck').show();
	  $('#logincheck').css('color', '#CC0000');
	  $('#logincheck').html('You must be logged in to submit.');
	  setTimeout("$('#logincheck').hide(); ", 3000); //display message for 3 seconds
   }
   else {
   	  document.frmPopMessage.submit();
   }
}
</script>

The CSS Code: