I actually understand how to change the style of a archive page via the body classes.
that is what i thought as well, therefore i pointed to category templates.
how exactly to make a new template file be called by different categories and if the code I posted above if the proper way to only display posts from a single category.
that would be a category template, as in the link i posted.
category templtes by default display the posts of a single category and of the child categories of it;
to really change that into a single category, you would need to add a bit of code before the loop;
something like:
<?php
global $wp_query;
$args = array_merge( $wp_query->query, array( 'category__in' => array( get_query_var('cat') ) ) );
query_posts( $args );
?>
http://codex.wordpress.org/Function_Reference/query_posts#Usage_Note