Contain the page content in a div and set the width and height to 1024 by 768 pixels.
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" >
<head>
<title>Untitled Page</title>
<style type="text/css">
.fixedSize
{
width:1024px;
height:768px;
/* use the below to centre the div */
margin-left:auto;
margin-right:auto;
/* set the background to red so we can see the div */
background:#ff0000;
}
</style>
</head>
<body>
<div class="fixedSize">
<p>Fixed Size!</p>
</div>
</body>
</html>