WhipE350,
I own a 2003 S that I just bought last summer, and it had the same problem with the light switch - I don't recall the dimmer stalk having anything to do with it. I was told the headlight switch is a common Boxster problem, and once I had the headlight switch replaced, everything has worked perfectly - and most importantly, when I wanted it to - not when it decided to.
Hope that helps.
Pat
