This will work with versions >=1.5.3, please note that this is just a example of the way to use the or statement.
<?php
  $connection = new Mongo();
  $db = $connection->test;
  $collection = $db->test;
  $collection->drop();
  $collection = $db->test;
  $apple = array(
    'fruit' => 'Apple',
    'type' => 'Juice',
  );
  $orange = array(
    'fruit' => 'Orange',
    'type' => 'Marmalade',
  );
  $collection->insert($apple);
  $collection->insert($orange);
  $results = $collection->find(array('fruit' => 'Apple'));
  foreach($results as $result)
  {
    echo sprintf("Fruit: %s, Type: %s%s", $result['fruit'], $result['type'], PHP_EOL);
  }
?>
Output:
Fruit: Apple, Type: Juice
Now an advanced search with "or" statement.
<?php
  $results = $collection->find( array( '$or' => array( array('fruit' => 'Apple'), array('fruit' => 'Orange') ) ) );
  foreach($results as $result)
  {
    echo sprintf("Fruit: %s, Type: %s%s", $result['fruit'], $result['type'], PHP_EOL);
  }
?>
Output:
Fruit: Apple, Type: Juice
Fruit: Orange, Type: Marmalade