message to user after complete POST

I have a POST form and action itself like following
<form name="MyForm"  id="MyForm" method="POST" action="index.php">
</form>

I want to show success message when POST complete or error message if there 
is any.
I would like to know are there any property or global variable I can check 
to show message to users.
If not, it seems that the only solution is jQuery, since it has success 
function that jQuery call after POST.

Your help and information is great appreciated,


Regards,

Iccsi,