sorry missed that part about the version.
also there seems to be a float on the .menu a in default.css that is causing the links to line up horizontally. your plugin is adding a .menu to the ul it creates, which then triggers the default.css stylesheet
.menu a{
float: none;
}
if you aren't already, you should try http://getfirebug.com
what about this:
function register_my_menu() {
register_nav_menu( 'primary-menu', __( 'Primary Menu' ) );
}
add_action( 'init', 'register_my_menu' );
function sidebar_menu() {
wp_nav_menu( array( 'theme_location' => 'primary-menu',
'container_id'=>'sidebar-menu',
'menu_class' => 'custom',
) );
}
add_action('thematic_abovemainasides','sidebar_menu');
for me this adds an unstyled list above the sidebar since i assigned the menu a class of 'custom' which doesn't exist yet in the css. or if you want to look similar to the sidebar styles you could add 'container_class' => 'aside', to the array.