Something

<?php
// $Id$

/**
 * Implementation of hook_menu().
 */
 function subdomainwizard_menu($may_cache) {
   $items = array();
   if ($may_cache) {
   $items[] = array(
   'path' => 'subdomainwizard',
   'title' => t('View the form'),
   'callback' => 'subdomainwizard_page',
   'access' => TRUE
   );
}
return $items;
}
/
/**
 * Called when user goes to example.com/?q=subdomainwizard'
 */
function subdomainwizard_page() {
  $output = t('Are you ready to create your subdomain?');
  
  // Return the HTML generated from the $form data structure.
  $output .= drupal_get_form('subdomainwizard_nameform');
  return $output;
  }
  
  function subdomainwizard_nameform() {
  $form['user_name'] = array(
  '#title' => t('Subdomain Name'),
  '#type' => 'textfield',
  '#description' => t('Please enter your subdomain.'),
  );
  $form['submit'] = array(
  '#type' => 'submit',
  '#value' => t('Submit')
  );
  return $form;
}

/** 
* Validate the form
*/
function subdomainwizard_nameform_validate($form_id, $form_values) {
  if ($form_values['user_name'] == 'King Kong') {
  // We notify the form api that this field has failed validation.
  form_set_error('user_name', t('King Kong is not allowed to use this form.'));
  }
  }
  
  /**
  * Handle post-validation form submission.
  */
  function subdomainwizard_nameform_submit($form_id, $form_values) {
  $name = $form_values['user_name'];
  drupal_set_message(t('Thanks for filling out the form, %name',
    array('%name' => $name)));
	}