You don’t have to. The driver runs in user-mode, so it doesn’t need any special privileges. However, it needs access to /dev/uinput. If your distribution doesn’t create a group for uinput access, you’ll need to do it yourself or just run the driver as root:
Is it possible in the future we can see the desktop on the tablet itself so we know where to touch the screen after lifting our finger?
Of course, that would be the killer feature. However, at the moment GfxTablet is only an input device and not a virtual screen. Implementing this would go far beyond the scope and possibilities of the current GfxTablet project.