Here is a nice and simple way to enable related products on a single product page when using wp e-commerce. There’s only four steps!
Step one: Download the “Related Posts” plugin from http://www.microkid.net/wordpress/related-posts/ and install it.
Step two: Set up the plugin and familiarise yourself with the admin panel. Here is a great place to start.
Step three: Insert the following where you want your related products to display (for me this is in the imported wpsc-single_product.php file in my theme folder)-
Step four: Change line 450 in microkids-related-posts.php (now in your wp-content/plugins/microkids-related-posts folder)
$output .= "<li><a href="".get_permalink( $related_post->ID )."">".$related_post->post_title."</a></li>n";
$output .= "<li><a href="".get_permalink( $related_post->ID ).""><img src="".wpsc_the_product_thumbnail(get_option('product_image_width'),get_option('product_image_height'),$related_post->ID,'single')."" ><br>".$related_post->post_title."</a></li>n";
And you’re done.