hmm
you can change the x11 config file (as root) if you are good at that (/etc/X11/XF86Config-4, back this file up before changing it as it can alter your display)

or you can apt-get a gui program that does it for you like:

cpad-kernel-dev - Kernel header for the Synaptics cPad driver
cpad-kernel-source - Source for the Synaptics cPad driver
tpconfig - configure touchpad devices
xfree86-driver-synaptics - Synaptics TouchPad driver for XFree86 server
ksynaptics - A KDE application to configure Synaptics TouchPad
qsynaptics - A QT application to configure Synaptic TouchPad


just apt-get it (like if you want tpconfig, the type in (as root) apt-get install tpconfig....) and run it
hope that helps