Sorry, I misunderstood what you meant. But note this still not a "standard" Windows function. That tab in Mouse Properties was added to Windows during the driver installation. Do you have the Windows 8 Synaptics Pointing Device driver installed?
Either way, I have not seen a notebook that did not allow you to disable the mousepad via a Fn key. And you only said "Gateway laptop" (no model number) so I cannot look yours up so again, check your key labels and/or manual.
I am assuming you want to disable this because you have attached a regular mouse to your notebook and you are tired of sending the mouse pointer across the screen when you accidently brush the pad with your thumb. What happens if you forget your mouse or it breaks, or the USB port the mouse is plugged into stops working? Can you navigate to that mouse properties page via keyboard alone to enable the pad again?
That's why it is best to disable with the Fn key combination. Again, look on your F keys. You probably will see one with a picture of a mouse or the mousepad. The image on my Toshiba F9 key shows the mouse pad with two buttons under it and a similar image with the universal symbol for disable (circle with a line through it) over the mousepad.