Hello,
basically the principle of payment gateways is very similar to that used in VirtueMart. The payment method is a plugin.
If you need to integrate with specific bank API, you need to adjust or create a plugin that deals with it. We deliver the PayPal, Moneybooker and DeltaPay with the component.
If you need own plugin, we can develop it for you as custom development. Or you can of course develop it yourselft, the API is open.