I remember that segment very well. I was already into the Atari 800 computers, so I recognized the 1200XL immediately even though I hadn't seen that particular model before. I think this was the first time I had ever seen a computer opened and explained in this way, and I always remember it whenever I explain computer architecture to my students today.
I'd highly recommend the entire Mr. Wizard's World DVD collection
. I picked up all eight volumes earlier this year. I don't believe they include every episode ever filmed, which is too bad, but they did manage to include lots of segments featuring classic computers. Besides the 1200XL segment, I remember a demonstration of a Vectrex light pen, a demonstration of Logo on an IBM PC, and a few segments featuring a TRS-80 Model 12 running some simple BASIC programs and an old word processor from Microsoft called Scriptsit. There were also a few shows which featured a Heathkit HERO 1 robot.