When you need to create a new transaction method for Drupal Commerce, you need to dive into the code. And that's something I have zero experience with. BUT the following couldn't be hard. I already created a new payment module (just copied and edited the payment example module so I have a new payment method).
commerce_payment_example.module you have the function
commerce_payment_ideal_transaction that is been executed by the submit button of the checkout form. The only thing I need to do is to execute a script on submit (in HTML you can do this with
<form method="post" action="script.php">, and pass three variables with it: the amount
($charge ?), the order ID
($order->order_id ?) and a description
($order ?). Could someone help me on the right way?