Wacom PenPartner serial graphics tablet won't draw

[irrevenant <irrevenant@netspace.net.au>]

I'm having a problem with my Wacom PenPartner serial graphics tablet.

Using the stylus moves the pointer around correctly, but pressing it 
down doesn't leave any marks beyond the odd random dot.  I've tested 
this in both The Gimp and Inkscape.  Drawing with the mouse works just 
fine.  I tried changing the threshold setting in XFree86-4, but it 
didn't help.

Does anyone recognise this problem, or have any ideas how I could fix 
it, please?

Here's what I've tried so far:

I'm running an (up-to-date as of 27-July-05) Debian Etch.

I installed the wacom-tools & wacom-kernel-source packages.  I used the 
Wacom-kernel-source config to build a package 
wacom-kernel-modules-2.6.11-k7 (which matches my kernel).  I installed 
that package.

I modified my XFree86-4 file to include the following:

Section "InputDevice"
   Identifier   "stylus"
   Driver         "wacom"
   Option         "Type" "stylus"
   Option         "Threshold" "2"
   Option         "Device" "/dev/ttyS0"
EndSection

Section "InputDevice"
   Identifier   "eraser"
   Driver         "wacom"
   Option         "Type" "eraser"
   Option         "Threshold" "2"
   Option         "Device" "/dev/ttyS0"
EndSection

Section "InputDevice"
   Identifier   "cursor"
   Driver         "wacom"
   Option         "Type" "cursor"
   Option         "Threshold" "2"
   Option         "Device" "/dev/ttyS0"
EndSection

I also added the following lines under the ServerLayout section:

InputDevice    "stylus"       "SendCoreEvents"
InputDevice    "eraser"       "SendCoreEvents"
InputDevice    "cursor"       "SendCoreEvents"


(It wasn't working at all using /dev/input/wacom so I used
/dev/ttyS0 instead).

Thanks.