我是这样做的：

/****** Add Thumbnails in Manage Posts/Pages List ******/
if ( !function_exists(\'AddThumbColumn\') && function_exists(\'add_theme_support\') ) {
    // for post and page
    add_theme_support(\'post-thumbnails\', array( \'post\', \'page\' ) );
    function AddThumbColumn($cols) {
        $cols[\'thumbnail\'] = __(\'Thumbnail\');
        return $cols;
    }
    function AddThumbValue($column_name, $post_id) {
            $width = (int) 60;
            $height = (int) 60;
            if ( \'thumbnail\' == $column_name ) {
                // thumbnail of WP 2.9
                $thumbnail_id = get_post_meta( $post_id, \'_thumbnail_id\', true );
                // image from gallery
                $attachments = get_children( array(\'post_parent\' => $post_id, \'post_type\' => \'attachment\', \'post_mime_type\' => \'image\') );
                if ($thumbnail_id)
                    $thumb = wp_get_attachment_image( $thumbnail_id, array($width, $height), true );
                elseif ($attachments) {
                    foreach ( $attachments as $attachment_id => $attachment ) {
                        $thumb = wp_get_attachment_image( $attachment_id, array($width, $height), true );
                    }
                }
                    if ( isset($thumb) && $thumb ) {
                        echo $thumb;
                    } else {
                        echo __(\'None\');
                    }
            }
    }
    // for posts
    add_filter( \'manage_posts_columns\', \'AddThumbColumn\' );
    add_action( \'manage_posts_custom_column\', \'AddThumbValue\', 10, 2 );
    // for pages
    add_filter( \'manage_pages_columns\', \'AddThumbColumn\' );
    add_action( \'manage_pages_custom_column\', \'AddThumbValue\', 10, 2 );
}