Hi
A payment gateway for Alpha Bank Greece is already built in to Cs-Cart since version 1.3.5
Now you can use installments (no interest) for versions 2.1.x and 2.2.x.
All you need to do is set your amount of installments and the price range for that installments (for subtotal over 200€ and under 500€, 5 installments etc) and you are done.
Customer can then choose in checkout to pay the whole amount at once or use the installments.
For Addon price and more information please contact as to info@dvs.gr
Fotis