Gary..........congrats on your winning the trip. You must have been at an SCI Chapter convention or something like that.
You will love Namibia, it is absolutely gorgeous country. As Pomoxis said, not all safari operators have a website and there are hundreds of them in Namibia and South Africa.
There is a website that has excellent information on Namibia, the game animals, visas, firearms import info and may even have info on Duiker Safari if you e-mail them. Check out the Namibia Professional Hunting Association at:
www.natron.net/napha/english/index.html
I too would recommend contacting the operator and inquiring about upgrading your hunt. Most of them are planning on you doing that when they donate a hunt to a convention anyways.
As Pomoxis mentioned......you will want to add kudu and springbuck. Others to consider are red hartebeeste, warthog and zebra (the Hartmann's are beautiful). There may also be an opportunity for eland and a few others, depends on the operator.
I really enjoyed hunting in Namibia and plan to return. Have fun!