Comment 4 for bug 34146

I had the same problem in Debian Lenny - I removed the PMax PMin and Pressure options in my Xorg.conf and it is almost perfect:
Section "InputDevice"
    Identifier "tablet"
    Driver "hyperpen"
    Option "Device" "/dev/ttyS0"
    Option "Mode" "absolute"
    Option "Cursor" "Stylus"
    Option "BaudRate" "19200"
EndSection

Now it senses about 1cm above the pad, but I have to actually touch the pad to make it click. I think that is about right for me, though I might try and play with the PMax and PMin to reduce the hight it senses the pen at

For the question of serial and ps/2, I think the data comes from serial, but it uses the ps2 for extra power - I could be completely wrong though