Hector Javkin , Jan 31, 2010; 03:53 a.m.
I have a D50 (also a D90) and a Nikon 70-300 f/5.6 VR IF ED. It's an excellent lens, lightweight, but built well enough, and handles very well with a D50. There's a discussion about it here on photo.net which contains two of my photos taken with it. The second of those was taken with a D50. For a safari, I would strongly recommend the 70-300 VR over the 55-200 VR. Even if the build of the two lenses were the same, and they're not -- the 70-300mm is better -- the extra 100mm of focal length will be very useful.
In fact, you might want more than 300mm, which isn't available new in Nikon in your price range. One possibility would be the Sigma 120-400mm OS (Sigma's term for VR) which many people seem to like, except for its heavy weight. It's available for about $900 at B&H. I don't have experience with this lens.
The other concern about the 70-300mm VR is its relatively small aperture of f5.6 at the long end. Within your price range, you can't do better at these focal lengths. However, you might want to make sure to have a lens of 50mm or so with at least an f/1.8 aperture for shooting in low light.
Finally, avoid the 70-300 non-VR. You will want VR for your trip, and the non-VR version isn't nearly as good optically. Have a great trip.