To add your stylesheet to the TinyMCE editor just add this as a filter. you can do this in your functions.php file.
/*
*
* Adds a filter to append the default stylesheet to the tinymce editor.
*
*/
if ( ! function_exists('tdav_css') ) {
function tdav_css($wp) {
$wp .= ',' . get_bloginfo('stylesheet_url');
return $wp;
}
}
add_filter( 'mce_css', 'tdav_css' );