Not the same problem as yours, but may be related:
I have finally acquired a driver to support my Kurta XLC 2436 digitizer in Windows 7. The product is Virtual Tablet by Digitizer Technology Company. When I start GCP with the mouse, I am able to activate the digitizer puck as well; it moves across the GCP screen just fine and acesses the menus. However, it is behaving as only a 3-button mouse, not a 16-button device. When I tried to assign a macro to a button beyond #3, using the MA command, nothing responds. Testing the Digitizer side menu on the screen I get a message that the program cannot find a digitizer when I select the DM command.
It is set to work through COM 1 and shares dutes with a 2-button Logitech mouse in W7.