special help needed for creating a new process whi

-- url of the page with the problem -- : www.tap-n-go.com/index.php/en/
-- Joomla version -- : 3.3.1

Hello,
I need your help in changing the registration / login process while payment is being made on my site. My site sells a software which is actually sitting separately, on a different server. During the payment process the buyer needs to enter his data including user name and password and the "next" button should send the parameters in post method to the system that manages the product, where it will be saved as user name and Password (and not on the site!) And only then he can move on to pay on paypal (This is the only payment method assigned).
By chance of a repeat customer, before the registration screen there should be a screen to enter a user name and password, the "next" button should send this data to the product management system and ensure the user is indeed registered. Only then will be payable on paypal without having to refill all the details. Please note that this is not the creation of a new user on the site at all!
Can you help in creating such a process and what will be your fee for the work?
Thank you,
Einat

Hello - Thank you for contacting us about this project. It's a good fit for our HikaShop development expertise, so I'll be following up with you privately via our ticket system.

Dear Einat,

I'll need some more details about the site where we need to register the user. Is it a Joomla site? Please send me the URL of it to sanjay @ deligence.com and then I'll come up with a proposal.

Dear Einat,

Did you get a chance to send an email to me?

Hi and thank you for your reply,
I'm still waiting for the answer of the guys that are in charge of the system (non Joomla) to respond. I will contact you when I get their explanations of what and how exactly they want the form to react.
Thank you!
Einat

Dear Einat,

Thanks for doing business with us. Looking forward to complete the project soon and to start a long term business partnership.