How do I disable the touchpad? I am running Vista Home Premium.
There is no Function key to enable/disable the touchpad.
I disabled the touchpad by going to Control Panel, Mouse, and disabling the touchpad device. But after I restarted the PC, the touchpad was enabled and the touchpad doesn't show up as a device when I use Control Panel.
In Mouse Properties, the only two items are PS/2 Compatible Mouse and HID-compliant mouse.

It is probably the PS/2 Compatible (Usually same protocol on the older built-in ones). The HID Compliant would be your USB mouse.

You could uninstall the drivers and then delete them and then ignore the error messages and be sure the settings are not set to auto install.

You could simply Disable the device hardware. Right Click "Computer," select "Properties" in the context menu. In the upper left corner choose "Device Manager." Expand "Mice and other Pointing Devices," right click on your device (Probably Synaptics something or other) and choose "Properties," go to "Driver" tab and click "Disable"

Some other things to try first:

Function+F7 is a common mouse disable combination (Sometimes F9)

With many Gateways, you could just tap (or double tap) the upper left corner of the touchpad to disable it.

You may also consider software alternatives such as TouchFreeze (https://code.google.com/p/touchfreeze/) or TouchPadPal (http://download.cnet.com/TouchpadPal/3000-2084_4-75012436.html) or Touchpad-Blocker (http://touchpad-blocker.com/).