Costumed Pages special excerpt

Hello every one, I have this Website that I am working on, and they have a few customized pages, which have their own portfolio section and we would like to have on each customized page an excerpt (on the back end), which will show in the portfolio section the excerpt which we did type at the back end. Does any one know how to do that? Or where should I look to learn how to do that? It could be an addition to “Custom Fields”

The code in the Function section has:

[code]

//Custom Post Types
add_action('init', 'create_myportfoliotype');
function create_myportfoliotype() {
$myportfoliotype_args = array(
'label' => __('Portfolio'),
'singular_label' => __('Portfolio'),
'public' => true,
'show_ui' => true,
'menu_position' => 5,
'capability_type' => 'post',
'hierarchical' => false,
'publicly_queryable' => true,
'query_var' => true,
'rewrite' => array( 'slug' => 'portfolio', 'with_front' => false ),
'can_export' => true,
'supports' => array(
'title',
'editor',
'post-thumbnails',
'custom-fields',
'page-attributes',
'author',
'thumbnail'
)
);
register_post_type('myportfoliotype',$myportfoliotype_args);
}

[/code]

I will appreciate your help. Please and Thank you.