Hi Steve,
We went to Tanzania in 2006, fantastic! There is lots of advice I could give, but regarding photography I notice you have the D50 same as me but I also had a 70-300 lens, and there were times when 400 might have been better. I was new to the camera and used auto quite a lot, however some of the results were ok. Take lots and lots of memory, you just cannot have enough! Batteries too, recharging was a problem but I managed on a couple of rechargeables. Each morning going out, the excitment was incredible and it was, for me at least, a photographers paradise. Possible suggestion is to shoot in jpeg rather than RAW, I am told your camera processes the info quicker for the next shot so you do not miss anything, and things can happen very quickly.
I wish I was going. If there is anything else I can help with let me know - where are you going to BTW?
Happy Shooting!
Mark