Looking at the source, here's what they did
first they remove the margin around the page body
PHP Code:
<head>
<title>9182 intro preview</title>
<style type="text/css">
<!--
body {
margin-left: 0px;
margin-top: 0px;
margin-right: 0px;
margin-bottom: 0px;
}
-->
</style></head>
Then they create a table that will fill the entire viewport of the browser by making the width and the height 100%. The background of the table is then set to the background image, it gets centered and repeats along the x axis.
PHP Code:
<table width="100%" border="0"
cellpadding="0" cellspacing="0"
style="background-repeat:repeat-x;
background-position: center; height:100%;
background-image: url(9182-1.jpg)">
Then they add a cell to the table and set the table alignment to center the content horizontally and vertically
PHP Code:
<tr>
<td align="center" valign="middle"> SWF GOES HERE </td>
</tr>
</table>
And that's it. As long as the background in the swf is also centered horizontally and vertically, the two should match up.