There are some tablet drivers that invert their 'Y' value on incoming tablet packets.
ArtRage uses the tablet packets to get higher resolution out of the stylus placement than normal mouse coords normally provide.
Most other applications use the mouse coordinates (and given the number of different interpretations many tablet drivers have of tablet packet data, I can see why!)
If you go to the 'Edit' menu, select 'Preferences', and switch on 'Use Mouse Mode', it should fix your problem.
AndyRage's mantra for graphics engine code:
"Sure - how hard can it be?"