Pen calibration problem under 1024x768 after installing XP SP3

I use Tablet PCs to record screen video during my lecture, for which I need
to set the screen resolution to 1024x768 (my screen is 1280x800). On Toshiba
M400, M700 and Fujitsu T2010, I need to calibrate the pen for 1024x768.
Recently the pen calibration stopped working in 1024x768 - a new blue
rectangle now appears (used to be blank, just a cross to tap on), but it
does not take calibration at all.

The only thing I can think about is that I installed XP Service Pack 3.

Another reason to use 1024x768 for me is that Powerpoint 2007 has bugs with
pen support in presentation mode when screen is in native resolution, the
recommended "fix" is to use 1024x768 for powerpoint show. I have installed
all office 2007 updates I can find, but still have that problem.

Please help,

Thanks,