First I'll assume you mean mouse support in the gui X windows enviroment. The configuration file can usually be found in /etc/X11/ and is usally call XF86Config and/or XF86Config-4 (depending on the version of x windows you installed). Inside that file will be the settings for the mouse, graphics card, and keyboard.
In XF86Config it should looke like this:
Section "Pointer"
Protocol "Microsoft"
Device "/dev/mouse"
ZAxisMapping 4 5
Emulate3Buttons
Emulate3Timeout 50
EndSection
If your system has a XF86Config-4 then it would look like:
Section "InputDevice"
Identifier "Mouse0"
# Modified by mouseconfig
Driver "mouse"
Option "Device" "/dev/mouse"
Option "Protocol" "Microsoft"
Option "Emulate3Buttons" "yes"
Option "ZAxisMapping" "4 5"
EndSection
If you have a ps/2 mouse the device should be be /dev/psaux. Make sure this part is correct. My guess is you have a ps/2 scroll mouse and accidently changed the device to serial. If you want more examples of mice configs, including how to make the scroll wheel / extra buttons work check out http://koala.ilog.fr/colas/mouse-wheel-scroll/#xserver
also you can search google for X windows mouse configs. If you still can't get it to work, post what type of connection and what type of mouse and I'll see what I can do. Good Luck.
