Under the Tablet PC settings, I believe there should be a BUTTON configuration tab that allows you to control what the buttons do and to activate them.
As you can see from the screen shot below, I don't have a buttons tab. I checked the drivers for human interface and Windows says its current. The driver date is May 2011 so it is probably current.
I can find no other options that would allow me to turn on this dialog. Does anyone have any suggestions?