Default image for WordPress Post Thumbnails

yes. open index.php and archive.php or any template and search this code
<?php echo dez_get_featured_post_image("<div class='post-thumb in-archive'>".$thepostlink, "</a></div>", 300, 300, "alignleft", "medium",dez_get_singular_cat('false'), the_title_attribute('echo=0'), false); ?>

change the last parameter to ‘true’ without quote and insert your default images in images/ name post-default.png. best size around 300×300

and rename custom-sample.css to custom.css and add this
#custom .has_no_thumb .post-right { margin: 0px 0px 0px 320px; }