for the custom background, you'd call
add_custom_background, for the cool header image things, it's
add_custom_image_header. You need to hook both those into something like
add_action( 'after_setup_theme', 'wpse27586_setup_theme' );
add_custom_image_header( 'some_callback_for_front', 'some_callback_for_admin' );
Add custom image header is more complex than it seems, so take a look in Twenty Eleven's
functions.php file inside the function
twentyeleven_setup, which starts around line 75, for some how to. The code is very well commented.