Create a 'photopost_migration' folder in sites/all/modules with photopost_migration.info and photopost_migration.module files that include the following code:

photopost_migration.info

name = "Migrate photopost"
description = "Module to migrate photopost content to Drupal 7"
package = "Development"
core = 7.x
dependencies[] = migrate
dependencies[] = migrate_extras
dependencies[] = field
dependencies[] = file
dependencies[] = image
dependencies[] = number
dependencies[] = text
dependencies[] = options
dependencies[] = taxonomy
dependencies[] = date
dependencies[] = date_api
dependencies[] = date_migrate
dependencies[] = link
dependencies[] = media

files[] = photopost_roles.inc
files[] = photopost_user.inc
files[] = photopost_board.inc
files[] = photopost_gallery.inc
files[] = photopost_forum.inc

photopost_migration.module

<?php
// $Id: migrate_example.module,v 1.1.2.4 2010/12/18 16:04:59 mikeryan Exp $

/**
 * You must implement hook_migrate_api(), setting the API level to 2, for
 * your migration classes to be recognized by the Migrate module.
 */
function photopost_migration_migrate_api() {
  $api = array(
    'api' => 2,
  );
  return $api;
}
?>