[jQuery] using getJSON() with IE vs FF

How should I get around the following?

For my jQuery exploration, I have a web page with the following body:

JSON: <div id="JsonDump"></div>

<script type='text/javascript'>
$(document).ready(function() {
  var url = "/code/jSystemMonitor.wcx";
  var secs = 5000;
  $("#JsonDump").ajaxComplete(function(request, settings){
    $(this).append("<li>"+settings.responseText+"</li>");
  });
  var res = $.getJSON(url);
  setInterval( function() { var res = $.getJSON(url); }, secs);
});

I'm basically testing the periodic ajax call and using this to begin
learning how to return JSON  and process it.   I started by just
appending the responseText into a div container.

Tthis works great under FF, every 5 seconds I am getting the JSON data
from the URL "/code/sytemmonitor.wcx" server-side applet.  Its a
simple applet that just print 1 line 5 fields in JSON format.

The first field is the current time (hh:mm:ss) and under FF I can see
that it is getting new JSON data every 5 seconds.

However, under IE, I am seeing the same JSON result over and over
again. Sounds like a IE caching behavior.

Whats the typical jQUERY way to resolve this fundamental getJSON idea
to make cross-browser ready?

Am I force to send an unique paramter value for each request to fool
IE the request is different?

Comments?

Thanks