Touch Pad/Tablet
The original XO-1 came equipped with a unique dual-mode pointing device. It functioned both as a conventional trackpad (the capactive-sensitive "Glide Sensor") and as a graphics tablet (the pressure-sensitive "Pen Tablet"). Starting in early 2009 this dual-mode pad is replaced by a regular trackpad without tablet support [1].
Basic information about how the touchpad is intended to be used can be found in the Human Interface Guidelines.
Hardware Specification
The hardware was manufactured by ALPS Electric. The specification (File:KGDMFA001-non-confidential.pdf) may require Acrobat reader with Japanese font package also installed for successful viewing and printing). See http://lists.laptop.org/pipermail/devel/2007-August/006080.html for missing details.
Disabling Touchpad
From a mailing list post, in Terminal Activity enter the command
xsetpointer -c "OLPC ALPS HGPK"
to disable the touchpad; enter
xsetpointer +c "OLPC ALPS HGPK"
to enable the touchpad (you don't need to be root).
PenTablet Software Support
No PenTablet support is planned at this time, and support is disabled in present kernels. However, it is possible to use the resistive touchpad from userspace without kernel support.