How do I access the variables posted in a page callback?
By default, Drupal looks for two functions on form submission (for forms generated with the Form API): {$form_name}_validate() and {$form_name}_submit();

For what you are trying to do, you need to implement the submit handler, do something with the form values (store to session, database, etc) and then go to page that will display the values of the form.  I've mocked up a quick and dirty module so you can see a couple different approaches:

function mymodule_menu(){

  $items = array();

  $items['sample_form'] = array(
     'title' =&gt; t('Sample Form'),
     'access arguments' =&gt; array('access content'),
     'page callback' =&gt; 'drupal_get_form',
     'page arguments' =&gt; array('mymodule_sample_form'),
  );

  $items['sample_form/success/%'] = array(
     'title' =&gt; t('Sample Form | Success'),
     'access arguments' =&gt; array('access content'),
     'page callback' =&gt; 'mymodules_sample_form_success',
     'page arguments' =&gt; array(2), //pass value of field_two to callback function
  );

  return $items;
}

function mymodule_sample_form($form, &amp;$form_state){

    $form['field_one'] = array(
      '#type' =&gt; 'textfield',
      '#title' =&gt; t('Field One'),
    );

    $form['field_two'] = array(
      '#type' =&gt; 'textfield',
      '#title' =&gt; t('Field Two'),
    );

    $form['submit'] = array(
      '#type' =&gt; 'submit',
      '#value' =&gt; t('Submit'),
    );

    return $form;
}


function mymodule_sample_form_submit($form, &amp;$form_state){

  //This is where you process and store submitted values.
  //Lets use variable_set to store the value
  variable_set('mymodule_field_one', $form_state['values']['field_one']);

  //Ok, lets now redirect the user to the success page and pass field_two as an argument
  $form_state['redirect'] = url('sample_form/success/'.$form_state['values']['field_two'], array('absolute'=&gt;true));
}


function mymodules_sample_form_success($field_two){

  $output = 'Value for field one: '. variable_get('mymodule_field_one').'&lt;br /&gt;';
  $output .= 'Value for field two: '. $field_two.'&lt;br /&gt;';

  //Lets display the form again, rebuilt.
  $output .= drupal_render(drupal_get_form('mymodule_sample_form'));

  return $output;
}