Interface is Parallel at device side, to serial at computer end of cable.

I did note that this site already has two drivers for this device, however the one that was specifically written for this device (sketchpro.zip) doesn't seem to like XP, and the other driver (VTablet), which has positive feedback about it's compatability with the device, is missing when I click download.

Support Information:
Device Type: Input Devices (mouse, etc.)
Manufacturer: Hewlett Packard (HP)
Model: SketchPro Tablet (Model 45911B)
Interface: Other
Operating System: Windows XP Professional
Age of Device: < 2 years old
FCCID: DSI6XU45911B

Find it on DriverGuide (http://members.driverguide.com/index.php?action=srch&sm=b&aax=&qa6=456&qa5=9&qa7=1500&dp=2&qm0=SketchPro+Tablet+%28Model+45911B%29&jmd=and&fzz=d) | Find it with Google (http://www.google.com/search?hl=en&lr=&ie=UTF-8&oe=UTF-8&q=Hewlett+Packard+%28HP%29+Input+Devices+%28mouse% 2C+etc.%29++SketchPro+Tablet+%28Model+45911B%29+Wi ndows+XP+Professional+DSI6XU45911B) | Research manufacturer Hewlett Packard (HP) (http://members.driverguide.com/index.php?action=getinfo&companyid=456)

I'm looking for SketchPro driver too. THe DB25 connector on the SketchPro is an old style serial port, not parallel, BTW.
I think any mouse driver might work, at low level but then need something else? Switch settings for BAUD rate would be nice to know.
G