Each card processor will probably have significant enough differences in the information required (and especially where to send the data) so a good approach may be to have a standard transaction module that then hands off the authorisation to a module specific to an individual payment processor.

Some of the processors (certainly the 2 big UK ones) have their own secure pages you can forward the cardholder to (including transaction amount, merchant id etc) so the cardholder enters details on the payment company's SSL-secured page and some confirmation code is sent back to the merchant's site.