Do you have the eeepc-acpi scripts installed? I use these with debian and both Fn-F3 and the touchpad button on the topleft successfully disable the touchpad. It looks like there is hope! :-)
If you do have these installed, which version are they?
What happens if you manually source /etc/acpi/lib/touchpad.sh ?
EDIT:
Ok. Manually sourcing that file won't help you to diagnose anything as it needs to be sourced from other files that are run by the hotkey handlers.
A good place to start is to run
and see what is output when the touchpad hotkey is pressed.