I think you should install the package inputattach and use that program to configure your serial mouse.

Example: I have got a serial Logitech mouse with a wheel plugged-in on COM1. Thus I would enter the following command in a terminal.
Code:
sudo inputattach --daemon -mmw /dev/ttyS0
The manual page explains which serial devices are supported. You could also enter
Code:
inputattach --help
to get a list of supported serial input devices.