To set up the Microsoft IntelliMouse PS2 WheelMouse, in /etc/X11/XF86Config-4:
Section "InputDevice" Identifier "Generic Mouse" Driver "mouse" Option "CorePointer" Option "Device" "/dev/psaux" Option "Protocol" "ImPS/2" Option "Emulate3Buttons" "true" Option "ZAxisMapping" "4 5" EndSection