Try giving the SimpleViewer gallery dimensions of 100% x 100% and then specifically giving the <td> into which SimpleViewer is embedded the width you'd like the gallery to be, eg:

<td style="width: 800px;">

There are also a few HTML errors on the page which should be fixed.
You can validate your page using the W3C Markup Validation Service: http://validator.w3.org/

The button bar (including the 'Open Image in New Window' button) is not visible in the landscape gallery.
Try clearing your browser's cache before reloading the gallery.

At the end of the second tab section, you have a <td style="width: 800px"> tag which looks like it should be a closing </td> tag instead.
Also, your first and second tabs are each in individual tables but the third tab is not.
For consistency, they should all be similar.
With regard to the differing widths, try duplicating the width in both the gallery dimensions (in the embedding code) and the CSS for the <td> tags.

It looks like you have not yet tried my suggestion of duplicating the width in both the gallery dimensions (in the embedding code) and the CSS for the <td> tags.
eg:

<h2 class="text">Matua</h2>
<p class="font1">New Zealand Wine Growers and Wine Makers</p>
<table width="880" border="0" cellspacing="0" cellpadding="0">
    <tr>
        <td style="width: 800px;">
            <!--START SIMPLEVIEWER EMBED.-->
            <script type="text/javascript" src="http://www.nzphotos2u.com/matua_glry/svcore/js/simpleviewer.js"></script>
            <script type="text/javascript">
                var flashvars2 = {};
                flashvars2.baseURL = "http://www.nzphotos2u.com/matua_glry/";
                simpleviewer.ready(function () {
                    simpleviewer.load("sv-container2", "800", "100%", "000000", true, flashvars2);
                });
            </script>
            <div id="sv-container2"></div>
            <!-- END SIMPLEVIEWER EMBED -->
        </td>
    </tr>
</table>
<p>&nbsp;</p>

Also, as an alternative, you could try embedding the galleries using the <iframe> method (rather than the baseURL method) described here: http://simpleviewer.net/simpleviewer/su … l#external

My suggestion was to duplicate the width in both the gallery dimensions and the <td> tags.
Although the width is set in the <td> tags, your galleries still have lines such as:

simpleviewer.load("sv-container2", "100%", "100%", "000000", true, flashvars2);

I intended for you to try:

simpleviewer.load("sv-container2", "880", "100%", "000000", true, flashvars2);

Keep each gallery in a separate folder (as they already are), and, rather than use the standard embedding code with a baseURL to point to the gallery folder, use the following <iframe> code (with the 'src' of the <iframe> pointing to the 'index.html' file in the gallery folder) to embed a gallery:

<iframe src="http://www.nzphotos2u.com/matua_glry/index.html" width="800" height="600" frameborder="0" scrolling="no"></iframe>

Instructions for this method of embedding (using an <iframe> to embed an external gallery folder) can be found in point #2 here: http://simpleviewer.net/simpleviewer/su … l#external