After LOTS of mucking about I found this driver/utility for a Summagraphics Summasketch III tablet that runs the Genius "Kids Designer" serial port tablet under XP perfectly for me. You can now easily change the functionality of the 2 buttons.
The original 3.11/Win95 driver described itself as the Trust Whacky Kidspad driver. So this driver may work for that tablet too. When I installed, it detected my pad as a "Learn-N-Sketch". Now I have Kidpix Studio and Kids Designer tablet running properly on my old XP laptop again!