You may arrange to pick up your vehicle anywhere in central Windhoek or at the International Airport (Hosea Kutako) which is 42km east of the city along the B6. So you are unlikely to need directions to Desert Car Hire.
If you should need to visit, the map below should provide sufficient directions to find Reginald Walker Street (marked with the green flag) either from central Windhoek or from the airport. GPS Co-ordinates: S22 36.111 E17 06.201
NOTE: Eros Airport IS NOT the International Airport.