I just had a strange experience with my 2006 987 Tiptronic.
I just took the car out of winter storage. I thoroughly cleaned and dusted every part of the car and started it up. Right away I could tell something was wrong.
When I shifted into reverse the car started moving forward. When I shifted into drive the car went in reverse. When I stepped on the brake the engine revved, and when I stepped on the gas pedal the brakes went on. When I turned the steering wheel to the left the car turned right. When I turned the steering wheel to the right, the car turned left. When I turned the radio volume up it got softer, and when I turned the volume down it got louder.
I didn't know what to do, so I called the dealer service department. The service manager listened to my description and asked me if I had removed any fuses recently. I told him that I always remove all the fuses and clean them when I take the car out of winter storage. He told me that starting in 2005 the boxster has a main directional fuse that controls the direction of the electrical current. He said if it gets put in backwards, everything on the car works in reverse just like I was describing. He told me which fuse it was (#103 on the bottom of the fuse box).
I took that fuse out, turned it around and replaced it. Now the car works perfectly.
If you have a 2005 or newer Boxster, be careful with your fuses!