September 10, 2012, 1:47 PM — Here's how you can tell OS X Mountain Lion to disable your built-in trackpad if you plug in a mouse or wireless trackpad.
1. Go to System Preferences.
2. Click on Accessibility.
3. Click on Mouse & Trackpad on the left side.
4. Click the "Ignore built-in trackpad when mouse or wireless trackpad is present."
For more, see the original article at the link below.
Disable Trackpad OS X Mountain Lion | Help Desk Geek