Most contemporary Linux distros running X do not have an Xorg.conf file, as X as gotten very good at detecting hardware on start-up that they are generally no longer needed for a smoothly functioning GUI.
will tell you how to create one, but it would be best to read up on how it works
before messing with it. Also, make a backup of a working Xorg.conf file before making changes, so you have a fall-back position in case your changes break X.
If you provided a more detailed description of what whacky stuff you mouse is doing, perhaps someone here has encountered it before. Also, if you have another mouse to test with, you could rule out a hardware problem with that particular mouse.