Personally, I do not think that you can do much in 7 days.
South Africa is an enormous country and takes time to get around.
I will try to break my comments down under a couple of headings to make it easier to read:
at this time of the year has very short days and can be very wet, windy and cold.
area will be dry, cold at night but not bad through the day (unless you happen to be there when a cold front is passing through).
Probably the best time of the year to visit here as the heat and humidity is much more bearable. Daytime temperatures will usually be around the 25 degree centigrade mark dropping to around 18 at night. Definitely not cold.
Wherever you go, it is best if you can fly. Public transport is not the greatest and whatever you do, avoid the minicab taxis. You can get cheap air tickets on Kulula, 1 Time and Mango.
Hiring a car is vital to get around but you must remember to be aware that hijacking and smash-and-grab crime is quite bad. Certain intersections are known to be black spots for these and will usually have police signboards advising where they are. Keep your windows closed, your doors locked and valuables out of site.
Roads can be in a very bad state although the main intercity highways are usually good. Many of them are now toll roads. There are also a lot of fixed speed cameras, including those that calculate your average speed.
Driving is a great way of seeing the wonderful South African scenery though and I really enjoy it.
There may not be any places left but you could look at travelling on the Blue Train from Johannesburg to Cape Town. This is a 24 hour ride if you catch it in Pretoria and an hour or so less from Johannesburg. This is a luxury train with first class service on board.
Things to do:
People get confused when they come to SA on holiday. You probably do not want to go into the city. Most tourists head straight for the Sandton area which is actualy a seperate town north of Johannesburg. You could stay here and use it as a base to go to Pretoria to visit the Vootrekker Museum, the Union Buildings (I think they are still called that). There are official bus tours of Pretoria. You can also do one of Johannesburg which might be an eye-opener. For animals, there is a tour to the Rhino and Lion Reserve. A tour of Soweto is also a good idea. I found a site which has these and a lot of others on the web
Durban has miles of beaches and warm water. It has good surfing and snorkelling. Water clarity is usually better at this time of the year as there is little rain and the rivers are not spewing all sorts of rubbish into the sea.
is a fantastic day out. I have been there a couple of times. It is reasonably priced and there are many activities to enjoy. If you fancy a swim with the dolphins, remember to take you swimming costume with you.
The Valley of a Thousand Hills
is inland of Durban but has some fantastic scenery. There are plenty of roadside stalls selling local crafts and a couple of good places to eat and drink.
Oribi Gorge is a couple of hours down the South Coast but is probably well worth a drive. Apart from fantastic scenery, there is a good chance that you will see plenty of smaller game. It is also home to the longest 'long drop' in South Africa - a long drop for those who don't know what it is is an old fashioned bucket toilet.
There are plenty of other things to do around here and I would suggest a search on the internet.
This is place where most tourists go and who can blame them. Even n winter when it is at its worst it is great. Or at least I think so and I do not even come from this part of the world!
There are so many things to see and do, places to visit, wine to drink, good food to eat.
Firstly, a visit to a wine farm is a must but I would suggest using an official tour company as you can then taste as much as you like without having to drive.
Cape Point is a good place to visit and, if the weather is not too bad, a trip out to Robben Island might be enjoyable.
If you enjoy driving, you could make an early start and head of for Cape Aghulas, the southern-most point of Africa.
A short drive into the Winelands and you will find yourself in Stellenbosch, a beautiful student town with many buildings still in the Old Cape Durch style. Lots of little restaurants and bars too. Across the Cape Town to Johannesburg highway is Paarl which is also worth a visit.
From Cape Town harbour, you can get helicopter tours which will take you on scenic flights all around the peninsular. I think the float plane trips are also still available.
Of course, you cannot miss going to the top of Table Mountain.You can either walk up (you need to be fairly fit for this) or you can get the cable car.
Outside of Cape Town is the Spiers wine estate where there is a cheetah breeding programme. Expensive but worth a visit. The wine is not bad either
A trip to seal island is always fun, especially if the sea is a bit rough! No good if you suffer from sea-sickness.
There are so many more things which you can do in and around Cape Town but I have a meeting to go to so I need to wrap this up.
As you can see, there is way too much to do in just a week and I would seriously suggest that you spend the whole time in in one place. Surf the net a bit to plan your stay and then use official tour companies and a hired car and I can almost guarantee that you will not have a quiet day for your whole stay.
Enjoy it wherever you go. It is a wonderful country with some really friendly and helpful people.