Payment gateway

Hi,
I have a very serious questions for PHP pros.
I’m using the woocommerce plugin for my virtual shop. My problem is with the payment gateways. I work with third party credit company, and I need to call their pages once someone click on the pay botton.

So the problems are:
1) How to add completely new payment gateway with the needed code?
2) I tried ti change the woocommerce-functions.php and it didn’t help. I know that inside that file the checkout button name is located, and I want to try to add the call code which is:

try
{
// Call pay method
XXX::Pay(“XXXX”,
“XXX”,
125.99,
1,
Languages::Hebrew,
CurrencyType::NIS,
“XX232lsUU”,
“Test Item”,
1,
“http://havaya4u.co.il/Pictures/.jpg”,
“http://Havaya4u.co.il/Pliskin/”,
“http://Havaya4u.co.il/Pliskin/Response.aspx”,
false,
false,
false,
false);
exit();
}
catch (ZCreditException $zex)
{
$e = $zex->getPrevious();
if($e != null)
{
echo $e->getMessage();
}else
{
echo $zex->getMessage();
}
}
catch (Exception $ex)
{
echo $ex->getMessage();
}

http://wordpress.org/plugins/woocommerce/