It sounds to me like you just need to make a sym link from /dev/whatever to /dev/mouse. The script your using to configure your X setup should have configured this for you, but doing it by hand is more fun. Just type (from a bash prompt) ln -s /dev/psaux /dev/mouse
The /dev/mouse is sym linked to whatever hardware your mouse actually is. This provides a common interface to any program that needs the mouse, be it a usb, serial, or ps/2 mouse it can be accessed through the /dev/mouse link. The above example where I used psaux is for a ps/2 mouse, I dont know which device you link to for a USB mouse.
If your bios supports handeling USB HID's and you enable it, than I belive it will logicaly connect your USB to your psaux. I have done this before and am not quite sure how it works, but it's pretty damn cool.