Well, i've experimented with Gentoo lately, on a modular X11, so it seems that if i comment the Optin "Device" "/dev/mouse" from the xorg.conf file, the mouse works. I don't understand these kind of behavior, but nontheless.
Fedora and other distributions come with an already configured xorg.conf file, and that really is a problem from users that have Genius Optical Mouse, on the ps/2 port, which is not properly detected by X.