Hi AlienXAXS,
I'm the person who is in charge of the UI implementations. All the PT implementations are coded in the class called Rx_GFxPurchase.uc, look at the default properties section at the bottom, all the PT descriptions are there, and the PT mechanics are within that class.
In terms of graphics, they are created in flash, exported it through scaleform, and imported into the editor. they're a bit more work to get hang of it, so you have a work cut out for you if you want to work on that. Research scaleform and CLIK to get started.
I'll try post up some images to guide you guys on what goes on in PT and other User Interfaces later today. I'll probably tidy up the code and provide proper documentations as well. That'll be in the long run though.
In the meantime, reach out to me for any UI questions, and I'll try my best to assist you guys.