Well, if you have a serial mouse it should be in /dev/ttyS0 (com1 for windows) or maybe in /dev/ttyS1 (com2).
/dev/mouse is usually a symbolic link[*] to the mouse's file (lets say its /dev/ttyS0). /dev/psaux is where /dev/mouse should point if you have a PS/2 mouse.
So maybe its just a matter of deleting /dev/mouse and making the symbolic link again.
[Symbolic links are files that points to other files, like "Shortcuts" in windows. If you run "ls -l /dev/mouse " you should see something like:
lrwxrwxrwx blah blah blah /dev/mouse -> /dev/ttyS0
which means /dev/mouse points to /dev/ttyS0
See "man ln" for more info ]