You will have to edit your /etc/X11/XF86Config file using vi, emacs, kate whichever editor you like. You will need to have these lines in your XF86Config file, then you will be able to use the USB mouse or touchpad:
Section "ServerLayout"
Identifier "Default Layout"
Screen 0 "Screen0" 0 0
InputDevice "Mouse0" "CorePointer"
InputDevice "DevInputMice" "AlwaysCore"
InputDevice "Keyboard0" "CoreKeyboard"
EndSection
Then for your USB mouse:
Section "InputDevice"
Identifier "Mouse0"
Driver "mouse"
Option "Protocol" "IMPS/2"
Option "Device" "/dev/input/mice"
Option "ZAxisMapping" "4 5"
Option "Emulate3Buttons" "yes"
EndSection
Then for your Touchpad:
Section "InputDevice"
# If the normal CorePointer mouse is not a USB mouse then
# this input device can be used in AlwaysCore mode to let you
# also use USB mice at the same time.
Identifier "DevInputMice"
Driver "mouse"
Option "Protocol" "PS/2"
Option "Device" "/dev/psaux"
Option "ZAxisMapping" "4 5"
Option "Emulate3Buttons" "no"
EndSection
Then you will be able to use both at the same time or individually.
Good Luck
