W00T! ...... It worked
I had to: install the PowerPoint viewer that came with Office because I didn't already have it loaded, create three seperate presentations (#1-regular, #2-looping, #3-regular), then use a text editor to create the playlist. PowerPoint Viewer is required as PowerPoint itself no longer supports playlists.
Then I fired up the PowerPoint viewer, and had it open my playlist. It went through the first set of slides normally, with me clicking each time I wanted to advance to the next slide. Then it got to the second presentation, and it sat there looping indefinitely through the slides of that presentation. Next, I moved my mouse over the slide, and in lower left-hand corner an icon appeared that when clicked upon allowed me to "end show". The viewer/playlist then continued on to the next presentation, which again let me advance slides manually till completed. The whole time the viewer never closed, and I couldn't tell that it was switching between 3 different presentations.
Took me a while to figure out that moving my mouse over the 2nd presentation would give me that icon in the lower left corner, and that it would allow me to click and choose "end show" on just the current running presentation. Before figuring that out, I had tried to hit the ESC key, which unforatunately stopped the entire playlist script from executing and closed the viewer. There may be another way to have the viewer stop and then continue to the next presentation on the list, but I don't know that that is.
So, there you have it hulkMAD.... its possible after all! While there may be other/better ways to do this, thats what I was able to get to work for me given my limited knowledge of PowerPoint.
Hope this is what you were looking for, and that it will help you. If you need help with how the viewer works, creating playlists, or the presentations, let me know. Everything you need to know about it you should be able to find in the PowerPoint help as I did.