Windhoek
Since you mentioned Windhoek:
Namibia doesn't have radar. Most of the good ATCs have left the country. WHat is left, is an overworked bunch of people, who haven't made it anywhere else. There are 2 good ones left, you will recognise them, since you wouldn't have any problem understanding them (no african accent).
Before entering the airspace, have your estimates ready for: FIR, 100 NM WHV (Windhoek VOR 114.50), 50 NM WHV (=TMA) and destination. Listen well to the other traffic, not that there is much enroute at higher altitudes. Get a mental picture of what is going on around you, just in case the controller looses his. Sometimes they give you rediculous seperation, because many of the controllers can't work on radial AND DME at the same time. If you feel it is to your disadvantage, question it and help them out.
If you fly into Windhoek (Hosea Kutako) International (FYWH) you need 2 frequencies: 124.7 for area control and 120.5 for approach once you are inside the TMA. The published tower frequency is not active, approach does the tower job too.
Should your plane be small enough and you are heading for Windhoek Eros (FYWE) you will be handed over to Eros tower 118.7 once you are below FL145.
FYWH has got an ILS on rwy 26 and GPS approaches, FYWE is VFR only. But the weather in NAM is not really a concern, 300+ days of cavok per year.
Let me know, if you need more.