If you have the needed modules loaded you should access the mouse as /dev/input/mice. Unless compiled into the kernel you will need the modules hid, mousedev, and the module for your USB host controller, which should probably be uhci (or usb-uhci) or usb-ohci. If you have a USB 2.0 controller you should use the ehci-hcd controller.
You can try to see if the mouse works by issuing cat /dev/input/mice
and moving the mouse around. If it works you'll see trash characters on the screen. Press Ctrl+C to stop oogling the mouse nonsense.