Hi,
I did this in September 2007 and can thoroughly recommend it. You really need to take the Victoria Falls add on too as it's stunning; this also gives you the opportunity to cross the border into Botswana across what must be one of the world's most chaotic border crossings. A great experience.
As far as walking difficulties is concerned, I don't think this should be too much of a problem as most sites etc are visited by coach or 4x4. The only problem you may encounter is the walk from the hotel at Victoria Falls to the actual falls; there are quite a few steps and rocks, and possibly the visit to the Makuni Village where the ground is soft but very sandy.
Regards
Mark.