[Zope] Newbie:Credit-card question

Hallo, that's my problem: I'd like to build up a shopping-system that's working with credit-cards(it's the customers wish). It's the first time I have to deal with this. How is the checking of the valid credit-card-number being done?? Which institution must be contacted by the server?? In realtime ( I mean is the contact with the client browser being held)?? Is this possible with Zope and in which way?? Thanks for the help Sven -- Sent through GMX FreeMail - http://www.gmx.net