See http://kohanaframework.org/3.3/guide-api/ORM#property:_belongs_to
class Model_User extends ORM {
protected $_belongs_to = array(
'position' => array('model' => 'Position')
);
}
Now you can:
ORM::factory('User')->with('postion')->find()->position->name;
Or indeed, with an already loaded user (e.g. $user = ORM::factory('User', 1);
$user->position->name;