All the main access roads from neighboring countries are paved, and cross-border formalities are user-friendly. Maun is easy to reach from South Africa, Namibia, and Zimbabwe, but the distances are long and not very scenic. Gaborone is 360 km (225 miles) from Johannesburg via Rustenburg, Zeerust, and the Tlokweng border post. Driving in Botswana is on the left-hand side of the road. The "Shell Tourist Map of Botswana" is the best available map. Find it at Botswana airports or in airport bookstores.
Forget about a car in the Okavango Delta unless it's amphibious. Only the western and eastern sides of the Delta panhandle and the Moremi Wildlife Reserve are accessible by car; but it's wisest to always take a 4x4 vehicle. The road from Maun to Moremi North Gate is paved for the first 47 km (29 miles) up to Serobe, where it becomes gravel for 11 km (7 miles) and then a dirt road.
It's not practical to reach Chobe National Park by car. A 4x4 vehicle is essential in the park itself. The roads are sandy and/or very muddy, depending on the season.