$view_args = array(); //Array of arguments
    $display_id = 'block_1'; 
    $view = views_get_view('viewname'); //Name of your view
    $view->set_display($display_id); 
    $view->display_handler->set_option('items_per_page',5);  //Set the number of items to return
 
    $view->set_item($display_id,'filter','type',NULL);  // Get rid of any current node type filters.
 
    /*******************
    *  Below we construct the new filter array.  
    *  I got this be creating a test view and stealing this array from the export code.  
    *  It was located in the $handler->override_option('filters', array()) code of the export.
    *******************/
 
    $filteroptions = array(
        'operator' => 'in',
        'value' => array(
          'ctype_name' => 'ctype_name',  //Change each ctype_name to the machine name of your content type
          'ctype_name' => 'ctype_name',
         ),
      'group' => '0',
      'exposed' => FALSE,
      'expose' => array(
        'operator' => FALSE,
        'label' => '',
      ));
 
    $view->add_item($display_id,'filter','node','type',$filteroptions);  //Add the new filter back to the $view object.
 
    print $view->preview($display_id , $view_args);