I would definitely stay in Sandton, to the north of the city, as it seemed to me to be the nicest part of town.

I stayed at the Garden Court Sandton City hotel (part of the Southern Sun chain). Although it's "only" 3 star, the rooms are modern and very comfortable, breakfast was superb and it has a swimming pool. It's location couldn't be better, as just across the road is an enormous and very swish shopping mall and also Nelson Mandela square with some great places to eat and drink. Every time I got the bill for lunch or dinner, I couldn't believe how reasonable it was, and the food was top notch too. Had no problems with safety there. If you wanted something more luxurious, there were swankier hotels adjacent.

Getting around in Jo'burg is rather difficult as there's no trains, buses and very few proper taxi's from what I could see. In fact I'm not sure how they're going to cope with the World Cup next year. If you wanted to do a few local tours, you would need to book them at the hotel tour desk. Gold Reef City was good fun and you can actually go down one of the mine shafts and explore the tunnels with a guide. Montecasino is great for an evening, though a fair way from Sandton, so getting there might be a problem (I'm not sure there are organised excursions). You could also do Pilanesburg Safari park and Sun City comfortably in a day.

Another vote for Sandton. We stayed in the Sandton Park Plaza, just a short walk from Nelson Mandela Square and that suited us nicely for a couple of days. We were warned to be extra vigilant in the evenings, but never had any issues. As mentioned there is a huge mall attached to Nelson Mandela Square with a good food court and cinema.
After a couple of days our overland tour picked us up in Rivonia, where we stayed in a Road Lodge (big chain of SA hotels). I've since been told that Rivonia isn't the best area, but we found the locals friendly and enjoyed a couple of meals out with no troubles.

When we flew out of Joburg we stayed again in a Road Lodge just outside the airport perimeter. I must admit our tour guides during the overland trip through South Africa, Namibia, Botswana and Zimbabwe did a good job of warning us away from staying in Johannesburg itself.

Thanks for the replies guys - shall check out the hotels.

J'Burg is for a wedding in the Sandton area for a couple of days before heading for Port Elizabeth and the garden route to Cape Town.

Nivsy