Jquery:

<script type="text/javascript">
	$("#isLoading").hide();
	$(document).ready(
        function(keyPage, jsNum, aNum) {
		$("#isLoading").show();
                $.post("/PHP_FILE_TO_CALL.php", { delimiter: $("#delimiter").val(), dump: $("#dump").val() },
                function(response){
			$("#ajaxCol"+jsNum).html(unescape(response));
                });
		$("#isLoading").hide();
        });
    };
</script>

Then just do like in the html:
<span id="isLoading"><img src=ajax.gif></span>