Tanzania

Matt and I have been planning a trip to Chile and Peru next year... I've lately been thinking about visiting Tanzania instead.

If we went to Tanzania, we'd do some combination of climbing Kilimanjaro and doing some sort of safari. But I have no clue where to begin planning or getting information for such a vacation. Has anyone out there ever been to Tanzania? Did you use a tour group, or did you go on your own? Did you make arrangements beforehand, or just take it one day at a time?