I am in a state of disbelief. I booked IAD/JNB/DUR roundtrip and now am doing a trip to Namibia for a week at the end of the trip. I have purchased Windhoek/JNB tickets to get us to JNB in time for our flight home to the States. I called SAA in the States and they informed me, both in regular reservations and in Voyager that I have to buy a whole new ticket! I have decided to try my luck, just go, and try to bribe or talk nicely with someone in order to just delete that DUR/JNB part of the flight. I do know that they will cancel the JNB/IAD part of the ticket if we do not show in Durban, but I really thought that just letting them know was enough. Any one have any ideas or any experience with SAA on this>

No experience with SAA, but other airlines.
Usually when you don't show up for a flight the rest of your reservation is canceled. So by not flying DUR-JNB the JNB-IAD will be canceled.
If you have a paper ticket you likely will see a X at the JNB-IAD leg, wich means that this is a transit. So even if you are able to delete the DUR-JNB from the reservation and trow the DUR-JNB coupon away they still will see from the ticket that you are not allowed to start using the ticket from JNB.

So the best option likely is to get a JNB-DUR ticket to start your trip home from DUR - assuming the fare rules dont allow changing the return from DUR to an open jaw from JNB - which it seems from the responses you got.

Some people took airlines to court in germany for this and won, but in general you should be out of luck here.

Somebody here has more experience with SAA?