Are you talking about the USB-connected Big Red Button, with the word "STOP" on it, that was given to teams in 2010 or thereabouts?
If so, don't worry about it. It acted as a keyboard and I think it sent a keypress of Control-Alt-Escape, but its function was taken over by the space bar on the Driver Station computer. Any time the robot is enabled, pressing SPACE will do an emergency stop.
If you really like using an external button, the one at
http://usbbuttons.com/big-red-button/ should work great.