Hi I need a bit of advice on taking donations online for a charity website I am developing.

They have a merchant account and they don't want to use PayPal or Worldpay due to limitations with their online forms. I need to basically develop a secure page which takes credit card details. The bit I'm stuck on is, how do I send the details onto the bank so they can process it instantly?

Hope my question makes sense, I really have no idea about this