Creating an add to cart function from HTML to OScommerce

I have an HTML website and there is a checkout process which is running in a javascript popup. User selects options at each step and at the end of the steps system redirects user to a shopping cart where a product has already been added to this cart. But this shopping cart not suitable for my needs. I want it to add a product to an oscommerce website. Because I am able to work with oscommerce and have payment modules for oscommerce. This oscommerce website will not be public and home page will not be visible. Users only be able to reach shopping cart screen from HTML website. For details you can check www.maxispy.com. This is my website. No need any payment module or any payment gateway integration. I only need this HTML to Oscommerce shopping cart function. Please bid good prices. I want to pay 50 USD milestone at first then pay remaining at the end of the job. Thank you.