If you are staying in Krakow, there really isn't a need for a car and driver. Just take the local train from the main train station to Oswencim. Should take about 30-40 mins to get there. Once you there, you can take the shuttle bus (it's either free or very cheap, can't remember) or a taxi.

1 day is enough to see both camps (and you won't forget them for years) .

Salt Mines are a must-see as well.

There is a GREAT guide for Krakow and surrounding area at http://www.inyourpocket.com/poland/krakow/en/ . You can also buy a more detailed, printed version in the Krakow train station.