No reason to be nervous about driving in Switzerland - just study your international signage and don't speed. We drove from Basel to Lauterbrunnen on past trips and the trip goes along excellent, well marked roads populated with excellent drivers.
But as already mentioned it isn't really necessary to use a car to easily travel to Interlaken or Lauterbrunnen, and once you get into the mountains the car becomes less useful. If you were to stay in one of the small towns above the valley (magnificent views) you would end up leaving the car on the valley floor anyway.
A long weekend is a perfect length of time - it takes most of a day to get to the Jungfraujoch, spend enough time up there to make it make sense and then get back - and there are other interesting stops along the train ride up. The Trummelbach falls are a big chunk of a morning or an afternoon and a trip up to the Schilthorn along with walking down from Muerren to Gimmelwald and a lunch at some point is all of a morning or an afternoon. Makes me want to go back just talking about it.
Check Mr. Steves website for a description of the sights, maybe buy a book - or get it from your library to check out the details of the trains/cable cars.
Have fun!