Doesn't exactly count as a "tablet"... but I use a DS running a homebrew called DS2WIN that maps the DS's touchscreen to the mouse. I set all the screen update settings to "off" so all the bandwidth is reserved for sending the stylus movements to the computer.
I keep the stylus on the screen at all times and use the Z key for clicking.
I keep the stylus on the screen at all times and use the Z key for clicking.