The switch you need is an Audi/VW part, (the Audi logo and part number are stamped on the side of the switch) which, if you get it at the Audi/VW dealer will be significantly less expensive than getting it from the Porsche dealer, or it was when I got mine anyway. Around $35. The Audi/VW part number is 4A0-905-849-B. Very good instructions can be gotten here.
http://mike.focke.googlepages.com/ignitionswitchreplacement . or here.
http://industryfigure.com/berkeley/Porsche/ignitionswitch.htm Its a little cramped under there but not too bad once you figure out where those darn little screws are and how to hold your left arm jusssssttttt so to get to them. Took me less than an hour start to finish. Be sure to disconnect your battery and be equally sure you have your radio code!
Bob