Need details to implement a payment gateway

Hi,

I am planning to implement a merchant account system( payment gateway)
for my website inorder to help credit card processing.

Please do let me know the following:


1. I need to implement the service just like paypal or yahoo or
citibank.I should be able to offer services to smaller merchants by
being able to support merchant account hanlding. How do I do that?

2. What language should I use to implement this?? What all details
would be needed?

3. Pls do send me reference links or material on implementing this.


-Thanks,
SA