<script src="js/jQuery.js"></script>
<script>

function ajax(url, name)
{
$.post(url, { ajax: name });
}

</script>


<?php

print "<span style='cursor: pointer;' onclick='ajax(\"ajax.php\", \"asd\")'>
<img src='images/budynek.PNG' border='0'>
</span><br>


include("ajax.php");

<?php

if(isset($_POST['ajax']))
{
print "
<div>
aaaaaaaaaaaaaaaaaaaaaa
</div>";
}

?>

<script src="js/jQuery.js"></script><script type="text/javascript">
$({
  $("span").click(function(){
    $.post("ajax.php",{ajax:'asd'},function(returned){$("span").html(returned)});
  });
});
</script>
<span>Ten tekst zostanie zastąpiony, jak go naciśniesz</span>

[PHP] pobierz, plaintext 
<?
if(isset($_POST['ajax'])) print "<div>aaaaaaaaaaaaaaaaaaaaaa</div>";
?>
[PHP] pobierz, plaintext