I used this excellent how to by shawna last March
http://www.z4-forum.com/forum/viewtopic.php?f=2&t=49294&hilit=centre+trim+remove&start=15
and also lots of excellent photos here by christurbo:
http://www.z4-forum.com/forum/viewtopic.php?f=2&t=21134&hilit=cf+dash
Also, I have a pdf of BMWs CD changer installation instructions - I can email it if you want.
I had no trouble with the infamous clip and washer at all on the main dash panel but you must take the glovebox out as suggested which is just 6 screws. All the clips then become accessible to remove and then the dash panel is loose. The centre vents are a bit fiddly but I'd had these out before.
The main difficulty I had was rear centre door as the I found it difficult to get a screwdriver in to the torx screws as Shawna suggested but the pdf suggests the hinge will pull off. On mine there were 2 small screws in the hinge, undo these and then the door pulls off - quite clever really - then you can get easy access to the 2 torx screws.