Custom meta fields for specific custom type only

I’ve got a custom post type curiculum and a metabox that saves a value to a custom field. However this custom field is added to another custom post type (created by an e-commerce plugin) wpsc-product.

This is a snippet of the code that deals with the metabox. The question is, how to prevent the custom field being added to the wpsc-product?

/* Curiculum Date Metabox */
function curiculum_date_fields() {
if ( get_post_type() == 'curiculum'):
    global $post;
    $custom = get_post_custom( $post->ID );
    $curiculum_date_from = $custom["curiculum_date_from"][0];
    ?>
    <p>
        <label for="curiculum_date_from">Date:</label><br />
        <input size="32" type="text" name="curiculum_date_from" id="curiculum_date_from" value="<?php echo $curiculum_date_from; ?>" />
<?php
endif;
}

function add_curiculum_date_box() {
    add_meta_box("curiculum_date_info", "Event Date", "curiculum_date_fields", "curiculum", "side");
}

function save_curiculum_date() {
    global $post;
    update_post_meta($post->ID, "curiculum_date_from", $_POST["curiculum_date_from"]);
}
add_action('admin_init', 'add_curiculum_date_box');
add_action('save_post', 'save_curiculum_date');
add_action('publish_post', 'save_curiculum_date');

EDIT: Code for the curiculum custom post type:

add_action('init', 'curiculum_register');

function curiculum_register() {

$labels = array(
    'name' => _x('CV Events', 'post type general name'),
    'singular_name' => _x('CV Event', 'post type singular name'),
    'add_new' => _x('Add New', 'testimonials item'),
    'add_new_item' => __('Add New Event'),
    'edit_item' => __('Edit Event'),
    'new_item' => __('New Event'),
    'view_item' => __('View Event'),
    'search_items' => __('Search Events'),
    'not_found' =>  __('Nothing found'),
    'not_found_in_trash' => __('Nothing found in Trash'),
    'parent_item_colon' => ''
);

$args = array(
    'labels' => $labels,
    'public' => true,
    'publicly_queryable' => true,
    'show_ui' => true,
    'query_var' => true,
    'rewrite' => true,
    'capability_type' => 'post',
    'hierarchical' => false,
    'menu_position' => 7,
    'exclude_from_search' => true,
    'supports' => array('title','editor', 'custom-fields')
      );

    register_post_type( 'curiculum' , $args );
 }

EDIT: I also recommand you to use nonces to check your field before saving.

EDIT2: Nonces

Just before field, define a nonce :

wp_nonce_field( 'curiculum_meta_box_nonce', 'meta_box_nonce' );

Your saving function is not correct, use this instead :

  function save_curiculum_date($postid) {
    //stop if autosave
    if( defined( 'DOING_AUTOSAVE' ) && DOING_AUTOSAVE ) return;

    // if our nonce isn't there, or we can't verify it, stop
    if( !isset( $_POST['meta_box_nonce'] ) || !wp_verify_nonce( $_POST['meta_box_nonce'], 'curiculum_meta_box_nonce' ) ) return;

    // if our current user can't edit this post, stop
    if( !current_user_can( 'edit_post' ) ) return;

update_post_meta($postid, "curiculum_date_from", $_POST["curiculum_date_from"]);
}

The fields function is not correct, use this instead :

$curiculum_date_from = get_post_meta(get_the_ID(),'curiculum_date_from',true);
?>
<p>
    <label for="curiculum_date_from">Date:</label><br />
    <input size="32" type="text" name="curiculum_date_from" id="curiculum_date_from" value="<?php echo $curiculum_date_from; ?>" />