There are a few choices. Without AJAX, you can use JavaScript to set the location attribute of an IFrame, or two or three of them. That will issue a GET request to the server.
With AJAX, your JavaScript makes an invisible asynchronous call to the server and when the response comes back your script modifies the HTML DOM in the browser and the changes appear without refreshing the whole page. It's pretty magical, but not simple. See if the Prototype library
Introduction to AJAX gives you enough info to decide if you want to pursue it.
Let us know what you think.
This discussion probably ought to move to an HTML forum or something.