In your /etc/X11/XF86Config-4 (or without "-4") first define your touchpad by adding something like this:
Code:
Section "InputDevice"
Identifier "touchpad"
Driver "mouse"
Option "Protocol" "PS/2"
Option "Device" "/dev/psaux"
EndSection
The in Section "ServerLayout" insert this:
Code:
InputDevice "touchpad" "SendCoreEvents"