Add a new widget area

Hi..

I’m having trouble adding a new widget area to my theme. So far I have two and they have been installed as such

/*-----------------------------------------------------------------------------------*/
/*  Enable Widgetized sidebar
/*-----------------------------------------------------------------------------------*/
function mts_widgets_init() {
	register_sidebars(array(
		'name'=>'Sidebar',
        'id' => 'sidebar',
		'description'   => __( 'Appears on posts and pages', 'mythemeshop' ),
		'before_widget' => '<li id="%1$s" class="widget widget-sidebar %2$s">',
		'after_widget' => '</li>',
		'before_title' => '<h3>',
		'after_title' => '</h3>',
	));

}
add_action( 'widgets_init', 'mts_widgets_init' );

/*-----------------------------------------------------------------------------------*/
/*  Enable Widgetized Footer
/*-----------------------------------------------------------------------------------*/
if ( function_exists('register_sidebar') )
    register_sidebar(array(
         'name'=>'Footer',
        'before_widget' => '<div id="%1$s" class="widget %2$s">',
        'after_widget' => '</div>',
        'before_title' => '<h3>',
        'after_title' => '</h3>',
    ));

However I’d like to add another to the header. I have read a number of blogs on adding new widget areas though the methods suggested either don’t work or break the theme. Any help would be much appreciated… thanks!