Comment 22 for bug 209911

Finally!

It was just my lack of knowledge about how HAL works. xsetwacom still does not work for me, but I can set the xorg TwinView option by adding

  <merge key="input.x11_options.TwinView" type="string">horizontal</merge>

to the wacom section in /usr/share/hal/fdi/policy/20thirdparty/10-linuxwacom.fdi or by creating a new file in /etc/hal/fdi/policy with

<?xml version="1.0" encoding="ISO-8859-1"?>
<!-- this is probably a bit imprecise -->
<deviceinfo version="0.2">
  <device>
    <match key="info.category" contains="input">
      <match key="info.product" contains_outof="Wacom">
 <merge key="input.x11_options.TwinView" type="string">horizontal</merge>
      </match>
    </match>
  </device>
</deviceinfo>

Maybe this solves other problems, too.