To compliment to Glovebox Rebuild writeup done by surfboardfiller, here's a quick way of fixing a Glovebox that won't unlock.
To unlock the glovebox if it's on the car, push the key to the right (on RHD cars) when unlocking which should engage the lock mechanism.
http://www.youtube.com/watch?v=H-qHjT_V ... tube_gdata
