Hi, unfortunately we don’t have support for Windows XP. The system requirements for Tobii REX is Windows 7 or Windows 8, as you can see on this page.
One of the requirements for the Control Panel and Showcase is .NET 4. It might work if you download .NET 4 separately, see this link, but I’m not sure. I would recommend to consider an OS update. Your application deserves better than to run on a 13 years old OS. 🙂