Pull REALLY hard. If that does not work look near the top for the plastic pin that hold the top in place. Get a credit card and a screwdriver. Use the CC to protect the pintwork while you put the blade of the scredriver under the end of the pin and lever it out.
Rincewind, May 2007
Remove the two phillips screws first then inside hatch through gap in fabric trim you'll feel a plastic nut to undo with your fingers. this releases the whole of the rear cluster.
huwrob, March 2007
Go to halfords and get a bulb and ask them to fit it think its a couple of quid :)