Porsche don't seem to do a retrofit kit for the aluminium pack, although they do make them in carbon and various shades of wood. Therefore, you have to buy all the bits individually, and they are an arm and a leg. This will give you an idea: http://www.design911.co.uk/fu/pt67_514_-cma81-cmo110-ct351/Porsche/996--911--1997-05/996-TURBO-2000-05/Alloy--Silver-Interior/
What some people do is remove the parts, and have them sprayed in Arctic Silver (same as original "Aluminium" finish). Fine if you can do without the car for a few days. Forum member Vron did this and posted some pics a few years ago. You can see them here:
http://www.porscheclubgbforum.com/fb.asp?m=252847
and here:
http://www.porscheclubgbforum.com/fb.asp?m=239477