Phil,
Namibia and Botswana are two of the most stable and trouble-free places you will find anywhere in the world.
Botswana has incredible wildlife, vast areas of unspoilt beauty, and all modern conveniences. Everything works, there is no corruption, you can buy anything you want in modern supermarkets. Most of the main roads are tarmac, but once you get into the bush they deteriorate into some quite difficult sandy tracks. Botswana is mainly bush, rivers & the famous Okavango Delta.
Namibia is vast, and much more arid than Botswana. However, there are some incredible "must see" things.........Fish River Canyon, Sossussvlei (tallest sand-dunes in the world), and Etosha National Park (more animals than you can shake a stick at). There are some secret paradises there I won't tell you about in case others start to go!! Again modern, no corruption, and everything works. The roads tend to be gravel, but they are graded so often that driving is easy.
They both have large tourist industries, with lodges, camp-sites, tour-operators and the like, but you will never find yourself in a crowd. Namibia is really well geared up for the independant traveller, and self-drive hire cars, 4x4, with all the camping gear, roof tents etc, are readily available. Botswana is more geared up for the rich fly-in type tourist (low-numbers high-cost) but I go regularly independantly and it is very straightforward.
They are both paradise.
In 5 years time, when Zimbabwe has recovered from Mugabe, you will be able to add Zim back into that description. Even now you would have no problems as a tourist.........except perhaps with fuel and your conscience.
If you feel you want to "do" Africa.......go ahead and do it!!! It is wonderful, and these two countries are a beautiful place to start.
Mike