Did it!
Here’s how. In front-slider.php, wrapped the <img> in a div, and title in one.
<div class="thumb">
<img src="<?php echo $thumb_small;?>" alt="<?php the_title();?>" title="<?php the_title();?>">
<div class="captions"><?php the_title();?></div>
</div>
css to suit.
Then in slider.js (about line 41);
var g=$$('img',h)[0];
changed to
var g=$$('div',h)[0];
Actually I don’t know why I had so much trouble. Simple really…