Yes the pointer section is the one i was talking about.
IMPS/2 is fine but you see the ZAxisMapping thing
First of all, there should be an Option before it. Next, it along with the values, 4 and 5 should be in quotes, like this
Option "ZAxisMapping" "4 5"
Make this change and then see.
And oh, you will need to restarrt the X server to get those changes to take effect. A simple logout into the command line and then again a startx