Besids this site which is great you might want to try The Hunting Report Newsletter site, it requires a subscription but is well worth the price. Between it and this site you can learn all you need to.
I used Cabelas for my first trip but have done my subsequent trips my self, of course not everyone becomes as addicted to hunting in Africa as I am!
One word of caution based on my experience and that of friends who I have hunted with, unless you are a better person than we are and have stronger willpower sticking to a proposed list of trophies won't happen once you arrive. Everyone I have gone with has shot more than they intended to!
Good hunting and you will love Africa!!!
Yea Im thinking I need to go with some extra green because I have heard that before. And I know my willpower sucks lol