Ok, I think I figured it out, it seems to be working, but would be glad to hear your insights:
<?php // Loop which loads the slideshow</p>
while ( $loop->have_posts() ) : $loop->the_post(); ?>
<?php
$src = wp_get_attachment_image_src( get_post_thumbnail_id($post->ID), false, '' );
?>
<div class="mslide mslide-<?php echo $i; ?>" style="background:url(<?php echo $src[0]; ?>) no-repeat right top;">
<p> </div><!-- .mslide --></p>
<p> <?php $i++; ?></p>
<p> <?php endwhile; ?>