AbleCommerce Shopping Cart Software

Hello!
I'm trying to add a new payment gateway to ablecommerce.

I had no problems following the Authorize.net example
http://wiki.ablecommerce.com/index.php/ ... nt_Gateway
(I also downloaded the example authorize.net class from the forums)

...but my requirements are a little different.
Our bank gateway has its own form where the user must insert the credit card number.

The gateways like authorize.net seem to need that the user enter CC number into the ablecommerce form, and then those data are sent to the gateway.

What I need is a custom gateway that works like paypal or google checkout (the user is sent to the payment page on the bank website, so the CC# is not entered in merchant's website, and returns with transaction result to the ecommerce).
Is there a way to create/add a custom gateway which works like that?

Is there anybody who already developed a gateway for BANCA SELLA? (one of the most famous Banks in Italy for online payments)

Thanks for your help.

Daniele

Well that would differ from Authorize.net because you have to send customer to third party system for payments. First find that what is the requirement of Banca Sella for integration for example are they using HTML form posts to pass information from shopping carts into there systems. If this is the case then upon checkout you can create form with required data and post it to their desired URL and there may be some call back mechanism as well that you will be needed to handle in order to perform actions depending upon payment status returned by Banaca Sella.