Where in Africa will you be going?

I take it you aren't really interested in spending a lot of dollars on high end equipment. Depending on your budget, I would recommend either Canon or Nikon. My sense is that:
1. Canon has some nice lenses at the low end - particularly ones that have image stabilization.
2. Nikon has some good mid-range lenses
3. Both have excellent high-end glass, with Canon having more lenses with image stabilization.
4. Arguably, Nikon seems to have slightly better light metering and flash metering systems.

Anyway, I would recommend getting the Canon 75-300mm f/4.0-5.6 EF Image Stabilizer lens, a wide angle to short tele lens to round out your focal length coverage, and whatever Canon body you can afford. As a rough guide, you will shoot most of your wildlife photos in the early morning and late afternoon at 300mm wide open with ISO 400 film. Bring at least a couple of rolls of film for each day of your trip. As others have mentioned, you should think about bringing along a second cheap body as a backup. If you are going to East Africa - Kenya or Tanzania, I believe they use pop-top 4wd vans or land rovers so you should take along a photo beanbag on which to rest your lens - I just brought a small utility zippered mesh sack and filled it with beans purchased at a local market.

I also recommend going to the zoo with your new camera and practicing taking some pictures and seeing how the come out.