I'm currently working my way through setting up a migration from vBulletin 3.8 to Drupal 7 using the migrate module (2.2). Here's the code that I'm using that will hopefully be of use to other vBulletin users.

First of all, I've created a 'vbulletin_migration' folder in the sites/all/modules/migrate folder and added .module and .info files

I've named the .module file vbulletin_migration.module and it contains the following code:

// $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 vbulletin_migration_migrate_api() {
  $api = array(
    'api' => 2,
  );
  return $api;
}

I've named the .info file as vbulletin_migration.info and it contains the following code:

name = "Migrate vBulletin"
description = "Module to migrate vBulletin 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[] = link
dependencies[] = media

files[] = vbulletin_roles.inc
files[] = vbulletin_user.inc
files[] = vbulletin_forum.inc

As the second block of code shows, files called vbulletin_user.inc, vbulletin_forum.inc and vbulletin_roles.inc have also been created and put in the vbulletin_migration folder...more info about each of these in the following pages.