You need to edit /etc/X11/XF86Config-4

Code:
Section "InputDevice"
        Identifier      "USB Mouse"
        Driver          "mouse"
        Option          "Device"                "/dev/input/mice"
        Option          "SendCoreEvents"        "true"
        Option          "Protocol"              "IMPS/2"
        Option          "ZAxisMapping"          "4 5"
        Option          "Buttons"               "5"
EndSection
Likely you just need to change to /dev/input/mice
Desktop icons? I have no idea....