We'd like to drive Switzerland in our 4 days we have to blow. Taking train from CDG to Lausanne, renting a car and drive the Bern Oberland. Sound do-able? Best use of our four days from Paris?
I'm not sure why you want to drive to berner oberland. You can take the Golden Pass line to Interlaken - it's really beautiful and if you book in advance you can reserve the VIP seating which is pretty nice.
When you get to Lauterbrunnen you probably won't need a car, you'll be taking lifts and funiculars to most everywhere you will want to go.
I think you'd be better of without a car in the Berner Oberland, at least if the idea is to stay in the mountains. But perhaps you would to better to fly directly into Zurich or Mulhouse and take the train (or rent a car) from there.
Are you staying in Lausanne or leaving directly? Their is a 20E fee for driving in Switz-- the people are not happy with cars in major cities. What time of year are you going.