Depending on the keyboard, you may find running a couple of wires to the contacts under a keyboard will not work. A number of keyboards use magnetic switch. There is only a moentary pulse for each key pressed and one when it is released. If you hold a key down you dont have completed circuit like you would with a normal push button. If you want to listen to and talk to a keyboard you might be better of doing it from the ps/2 port side. ps/2 port is just a serial port at TTL level. Listen for the keypress. The LED can be controlled from the ps/2 serial stream as well.