Of course there is the Internet with its almost endless source of information on whatever one might need to know and yes, there is also lots of information on African safari countries. Wikipedia will know about Kenya and Tanzania and there will be links to additional websites to get more specific information, but it is just so nice and handy to have it all in one location. Especially specific travel information on visa requirements, vaccinations, climate and more, are what one would like to know before departing on African safari. One example for having it all in one place to view online, to download as PDF and to download as free iBook for iPad is right here.
Also travel guides like Lonely Planet or the Rough Guide are a good source for practical travel information. For visas, always check government websites. They have the up to date information, at least they should.