Problem Relating a Tutorial

Hello, (i’m new to BlenderArtists.org!)

I want to make a simple FPS game play and I looked for the Mouse Look script, I found this website http://www.tutorialsforblender3d.com/MouseLook/MouseLook_1_Introduction.html

I followed all the steps but when I look up, the camera look down? (when I look left, it look right as well) Is it possible to invert the mouse axis?