I have a mac mini running 10.5.7 do i need a driver or instal a program to make a pablo kg-pb20 to make it run properly. it has a serial connector with a usb adapter. the tablet works but has inconsistent tendencies and the mouse barely works. trying to get it to work with Gimp

I think you are pushing the proverbial uphill - the Gear tablets are really designed to work with Windows, especially the serial ones.
KB Gear went out of business a long time ago - before 2005. Trying to get a piece of hardware designed for an old version of a different OS is an exercise in futility.
Go buy a Genius or Wacom, throw the KB in the bin...