Answer by JohnP for Linking page in a div with html forms and php

Since you've tagged jQuery, I'll use a jQuery example

$(document).ready(function(){    $('form').submit(function(){       $('#content').load('code.php');       return false;    })})

This makes a couple of assumptions here

1. This assumes that code.php is in the same path that you are in now.
2. There is only one form in the page.
3. As @johnhunter points out, this example obviously won't work with post. You can send the post data along with the method. See here for usage : http://api.jquery.com/load

EDIT

Here's a fiddle example : http://jsfiddle.net/jomanlk/J4Txg/

It replaces the form area with the content from jsfiddle/net/echo/html (which is an empty string).

NOTE 2 Make sure to include the code in $(document).ready() or include it at the bottom of the page. It goes without saying you need jQuery in your page to run this.