Ive found the best tool for inserting in the small hole on the underside of the steering wheel boss is an 'uncut' silicone tube nozzle!
(be sure to remove the fuse first or you'll upset all your neighbours when you keep setting off the horn)
Slide the horn push/airbag module upwards towards the windscreen to expose the steering wheel nut (It's a Torx head bolt)
Ralphy, June 2011
not sure on your motor but the hole may be for a thin screwdriver to lever a wire clip to release the air bag and once off the nut/bolt for the wheel may be exposed
