i had same problem, you need to open the boot and put your hand behind the light cluster between the top of the wheel arch and the parcel shelf. feel for a plastic wing nut (below wiring plug), fully unscrew this and the 2 screws you already know about, there is a push fit clip which should come away when you hold top of the cluster from outside and pull hard. after this it is simple clips. if you have any problems let me know
stephen, September 2006