Update:

I have spoken to DirectOne, and they have informed me that the osCommerce copy of directone.php should be able to work with some adaptation.

I have copied those files as suggested, but get the following error in my manager when I open the payment module:

Fatal error: Call to undefined function: tep_db_query() in /home/content/i/n/e/XXX/html/shop/includes/modules/payment/directone.php on line 149

This relates to this bit of code:

function check() {
if (!isset($this->_check)) {
$check_query = tep_db_query("select configuration_value from " . TABLE_CONFIGURATION . " where configuration_key = 'MODULE_PAYMENT_DIRECTONE_STATUS'");
$this->_check = tep_db_num_rows($check_query);
}
return $this->_check;

Does anyone know how to fix this?

Many thanks,

Goshawk