Your best bet would be to contact the maker of your touchscreen and ask them if they have an SDK (Software Developers Kit). This will give you the headers, etc that interact with their hardware. You will probably still need to buy a compiler of some sort depending on the OS that the touchscreen is using. (Java, C++, etc.)
I hope this helps. (without much to go on)
Painting a GUI with most modern tools is pretty simple. You place your buttons and many of the IDE's will generate a framework of the application for you. You then have to hook the method that's driven by clicking on the button to your specific function. This is where the SDK comes in. Typically they would provide you with examples of how to send something out across the bus. Depending on how the wires are coming out of your touch screen (what type of connector, and what protocols it supports) the logic will vary.
Regards,
Dave