Rental cars are readily available in Sweden and are relatively inexpensive. Because of the availability and efficiency of public transport, there is little point in using a car within the city limits. If you are traveling elsewhere in Sweden, you'll find that roads are uncongested and well marked but that gasoline is expensive. All major car-rental firms are represented, including Avis, Hertz, and Sixt. Statoil gas stations also rent out cars, as do local Swedish companies such as Berras and Auto, which can sometimes have better prices than the major companies.
Approach the city by either the E20 or E18 highway from the west, or the E4 from the north or south. The roads are clearly marked and well sanded and plowed in winter. Signs for downtown read "centrum." Driving in Stockholm is often deliberately frustrated by city planners, who have imposed many restrictions to keep traffic down. Keep an eye out for bus lanes, marked with "buss" on the pavement. Driving in that lane can result in a ticket. Get a good city map, called a Trafikkarta, available at most service stations for around SKr 75.