Here is how I did to have multiple gallerys

* The structure
index.php
gallerys
.....gallery1
.....gallery1_thumbs
.....gallery2
.....gallery2_thumbs
   .
   .
.....galleryn
.....galleryn_thumbs
.....gallery1.xml
.....gallery2.xml
   .
   .
.....galleryn.xml
 
 
* Modify each xml file like this :
gallery1.xml put imagePath="gallerys/gallery1/" thumbPath="gallerys/gallery1_thumbs/
gallery2.xml put imagePath="gallerys/gallery2/" thumbPath="gallerys/gallery2_thumbs/
galleryn,.xml put imagePath="gallerys/galleryn/" thumbPath="gallerys/galleryn_thumbs/


* In my index.php I just call the right xml file depending on my menu

<?php
    if(isset($_GET['gallery']))
    {
        $indexGallery = $_GET['gallery'];
        echo "<div class='center' id='gallery'>";
        echo "<script type='text/javascript'>";
        echo "<!--n";
        echo "var strgallery = '/gallerys/gallery$indexGallery.xml';n";
        echo "var so = new SWFObject('/viewer.swf', 'viewer', '813', '650', '8', '#506E87');n";
        echo "so.addVariable('xmlDataPath', strgallery);n";
        echo "so.write('gallery');n";
        echo "// -->";
        echo "</script>n";
    }
    else
    {
        echo "<div class='center'>";
        include "texte.php";
    }
    echo "</div>";
?>