[arfa]

Still poking about.
I have a FF solution but no IE

<script>
$(function() {
$('<img>').attr({'src':'<?php echo $image; ?>','id':'bg','title':''}).appendTo('#bg-wrapper').parent().fadeIn(1000);
        var captions = [<?php echo $cap_array; ?>];
        var len = captions.length;
    $('.change').click(function(e) { 
    e.preventDefault();
            var img_now = $(this).attr("id").replace("tn_","");
                for (var i=0; i<len; ++i) { var file = captions[i].split("|");
                    if (file[0]==img_now) { var this_cap = file[1]; }} // works in FF but not IE

//var mytext=document.createTextNode(this_cap);
//document.getElementById("img_caption").appendChild(mytext); // Adds - but not replaces

 img_caption.innerHTML = this_cap; // seems OK in FF & IE - but no caption from loop. :(

    
    var image = '<?php echo $album; ?>/'+$(this).attr("id").replace("tn_","");
        $('#bg').parent().fadeOut(800, function() {
            $('#bg').attr('src', ''+image); 
              $(this).fadeIn(800); }); }); });
</script>

I suspect this may look a bit clumsy but I am a work in progress...
PS - an alert test on var len has FF=18 IE=17 - which is weird.