Configure MerchantOrderForm for new gateway

I need a coder who *has worked* with a pretty old shopping cart cgi script called MERCHANT ORDER FORM (see [login to view URL]) who can help me reconfigure it to interface with a new credit card processing gateway. I want to change from a "post" interface to API if possible. Also, there are a couple of configuration issues with the back end of the cart that need to be resolved so that the billing information screen passes the correct data on to the gateway.