We are going to Botswana, Masai Mara and Victoria Falls in a week. I am bringing my Nikon D80 with an IS80-400 tele and a regular zoom 12-70mm. I hear dust can be a problem. Maybe especially when changing lenses. Any feedback?

Get a D40X and use it for the 12-70mm. D40X costs about $600, a nice piece of change but not a huge amount compared with your safari cost. No changing lenses and you have a back-up body and camera for your companion (if they need one). Only downside is that it is more stuff to carry around.
regards - tom

It has just started raining a bit in Botswana - mentioned in a current thread. So, i'm sure the dust is settled.

Africagirl,I didn't know that Nikon made a 12-70mm lens but if that is the focal length, then I would put that on your D80 for Victoria Falls and save the 80-400mm for the Mara. Keep the camera and lens in a waterproff pillow case (Walmart variety) while traveling on dusty roads and change lenes as little as possible. Normally I would second Tom's suggestion but with only a week left before you leave, I doubt you are inclined to get a D40X. Still it's a good thought. The operating syetems are similar enough and so there is not much to the learning curve. You can always sell it when you return. If you opt not to get a second body, do take sensor cleaning supplies and try them out before you leave.
Regards-Chuck

Do try to avoid changing lenses in dusty places, but sometime it is necessary. cary a sensor brush lik ethe artic butterfly (way overpriced) or a sensor sweep (equally effective.

Thank you everyone for your good advice. I do have a D70 body which I was going to leave at home because of the weight. We are limited to 44lbs. for everything and I am at 19lbs. before I even pack a t-shirt. But...how many times do you do to Africa? Maybe I'll just wear the same clothes over and over again.
And Tom, you're right. The shorter lens is an 18mm-55mm.