Thank you! I installed a trial version of PowerShow and it solved the problem.

Kinda.

I followed the directions for starting the slide show on the second monitor, but it's still starting it on my primary. I'm able to shift it over to the second monitor using ctr+win+x, but then the resolution is all manner of messed up. At least I can use my primary monitor now, but I cannot seem to get to image size / aspect ratio correct on the second monitor (even when all the settings are correct...)

But thanks all the same. I'm sure I'll get there soon.