Some of the areas you drive through to get there are a bit sketchy. (Tugela Ferry comes to mind). Some like to do their own thing, but going with a specialist guide is well worth it. You don't necessarily need to go with a group, guided tours for small groups (one or two people) are available and not that expensive.
We went from Durban, and the guide we went with took us out one way and back another, so we got to see a few extra things as well. For example, the "ultimatum tree" where the war really started, because it was here that the Zulus were given the unacceptable terms that led to the actual declaration. We also went through an area where the major battle of the Bombata rebellion was fought.
Even if you go with a guide, it is good to have done some homework before hand. The Osprey military books have a great chronological illustrated guide to the battle. Again, with Ian Knight doing most of the writing. Maps out the various manouvers with a really good 3d map of events. Wish I had it with me when I walked the battle site.