As a tourist, there is no reason at all to try a private car in the center of Berlin, it is much easier to get around by public transport. With Berlin WelcomeCard it will even be very cheap - save money!
The card is not just a travel card that for a one-time expense lets you drive as much as you want during the period it applies. It also provides significant discount at more 200 places.
You can choose to get a WelcomeCard that is valid for 48 hours, 72 hours or 5 full days - and you can choose whether it should only apply to Berlin itself or whether Potsdam should also be included.
The card can be bought in several places in Berlin at hotels, tourist agencies and the like, or you can save yourself the hassle and buy it online even before you leave home. It's easy enough to walk on theirs online shop and buy, but be a little careful because there are many choices.
In addition, you also get a small pocket guide for tourists with lots of local knowledge and current suggestions for activities, an overview map of Berlin and Potsdam, as well as a map of public transport in the same area.
Prices range from 17 € to 35 € (May 2012) per person.