Touchpad

It's very easy to tell X to use two mice together. You'll have
to add a PS2 mouse to your XF86Config-4 in addition to an USB mouse
(if you use one that it).

The entries should look like this:

Section "InputDevice"
        Identifier      "USB Mouse"
        Driver          "mouse"
        Option          "CorePointer"
        Option          "Device"                "/dev/input/mice"
        Option          "Protocol"              "ImPS/2"
        Option          "ZAxisMapping"          "4 5"
EndSection

Section "InputDevice"
        Identifier      "Touchpad"
        Driver          "mouse"
#       Option          "CorePointer"
        Option          "Device"                "/dev/psaux"
        Option          "Protocol"              "ImPS/2"
        Option          "Emulate3Buttons"       "true"
        Option          "ZAxisMapping"          "4 5"
EndSection

Section "ServerLayout"
        Identifier      "Default Layout"
        Screen          "Default Screen"
        InputDevice     "Generic Keyboard"
        InputDevice     "USB Mouse"
        InputDevice     "Touchpad"
        
EndSection

Files of interest: XF86Config-4