Hi Steven, thank you for your prompt reply. I have now updated one of my gallery.xml files to the new format but now none of the files display at all on both the normal Flash viewer and the iPhone.

The gallery I have updated can be found here: http://www.helenparris.com/g_cenotes.php

An extract of the gallery.xml file is below:

<?xml version="1.0"?>
<simpleviewerGallery maxImageWidth="640" maxImageHeight="640" textColor="0xFFFFFF" frameColor="0xFFFFFF" 
frameWidth="10" stagePadding="40" navPadding="40" thumbnailColumns="3" thumbnailRows="3" 
navPosition="left" vAlign="center" hAlign="center" title="Cenotes" enableRightClickOpen="false" 
backgroundImagePath="" imagePath="cenotes/photos/" thumbPath="cenotes/thumbnails/">

    <image imageURL="photos/000274.jpg" thumbURL="thumbnails/000274.jpg" linkURL="" linkTarget="">
        <caption>Carwash Cenote, Tulum, Mexico (C01)</caption>
    </image>
    <image imageURL="photos/000308.jpg" thumbURL="thumbnails/000308.jpg" linkURL="" linkTarget="">
        <caption>Gran Cenote, Tulum, Mexico (C02)</caption>
    </image>
.....

Great stuff that worked. Thank you!

Is there anyway I could make these links relative though? I am trying to keep the file as simple as possible (as it's not me who has to edit it).

The links are already relative (to the HTML page into which the gallery is embedded).
The alternative would be to use absolute URLs such as http://www.helenparris.com/cenotes/photos/000274.jpg

If you want to keep the relative links as short as possible, then you could:
(1) Create your gallery (perhaps using svBuilder-Pro)
(2) Upload your complete gallery folder (not just the contents)
(3) Embed the gallery using the baseURL method described here

The relative links (the imageURLs and the thumbURLs) within the XML file will then become relative to the baseURL (rather than the HTML page itself).

Yes. Please see the top of the FlashVar Options section of the 'SimpleViewer-Pro Config Options' page for details.

An example (to set the frameColor and frameWidth via flashvars) would look like this:

<!--START SIMPLEVIEWER EMBED.-->
<script type="text/javascript" src="svcore/js/simpleviewer.js"></script>
<script type="text/javascript">
var flashvars={};
flashvars.frameColor="0xFFFFFF";
flashvars.frameWidth="10";
simpleviewer.load("sv-container", "100%", "100%", "222222", true, flashvars);
});
</script>
<div id="sv-container"></div>
<!-- END SIMPLEVIEWER EMBED -->

Please note that your gallery's XML file still uses attributes from SimpleViewer v1 which are no longer used in SimpleViewer v2. SimpleViewer v2 will interpret them as best it can if there is a direct equivalent but where there is not (for example with navPadding) you may need to tweak your gallery's layout using the available nearest equivalent v2 options. To be sure of no surprises, it would be best to simply use only v2 options. Below is a list of your v1 options and the nearest v2 equivalents:

navPadding -> stageHPadding & stageVPadding
navPosition -> thumbPosition
hAlign -> stageHAlign
vAlign -> stageVAlign
thumbnailColumns -> thumbColumns
thumbnailRows -> thumbRows
stagePadding -> stageHPadding & stageVPadding

Please see the SimpleViewer-Pro Config Options page for a full list of SimpleViewer v2 options.

When viewing a SimpleViewer gallery with the Mobile Player in 'Full Window' mode, SimpleViewer uses the 'full.html' file within the 'svcore' folder, which is where the 'SimpleViewer Gallery' title is coming from.
Just open the 'full.html' file in a plain text editor and edit the contents of the <title></title> tags.