There are a few ways to go about this...
The mouse configurations are set in the XF86Config file which is located
at /etc/X11/XF86Config. You could, go into this file and change the settings
from the USB mouse to the PS/2 (aux) mouse or touchpad.
A better way...
An easier wasy is to just start up Yast and let it do the work for you.
You can get to a prompt by hitting CTL-ALT-F2 at the login screen.
From there, login, then login as su, and start yast by typing yast2
at the prompt. From there, you just navigate to to mouse selection, and
change it to PS/2 (aux port) or something like that. After you configure
the mouse you can get back to the login screen by hitting CTL-ALT-F7.
Try out your mouse back at the login screen and see if it works...
Try out Yast2 and let me knwo if it works out...