Add the ums driver to the kernel.
moused -p /dev/ums0 -t auto
Use the first USB mouse on the system as your console mouse.
Change the "Pointer" section in xorg.conf to the following
to be able to use the USB mouse under X. When using the XiG accelerated X server, change the mouse device to /dev/ums0 and the mouse type to "MouseSystems".
If you want to be able to use the mouse in both virtual consoles as well as in X change it to:
ohci(4), sysmouse(4), uhci(4), usb(4), xorg.conf(5), moused(8)