Although neither of these replies address my problem, I did solve it myself. It was due to overly long filenames. Audio players all work with very long filenames, but Office 2003 limits them to 42 characters. Renaming files did the trick. This was not easy to discover!
Jinny, there is a way to save files in the earlier format. You can even set it to do that by default. So you don't need Office 2003. Also, if people who don't have Office 2007 install OpenOffice, they'll be able to open the DocX format or whatever it is. That's how I handle them.
Guereoro, I found a terrific program last night, totally free, that works slick as a whistle to convert PPT files to SWF. It's
iSpring Free, and it works inside PowerPoint. Most excellent. The only indication it is involved is the discreet iSpring logo on the Flash player built into the DNA of the converted file. I love the program so much I'm happy to let them do that. My files convert flawlessly and are equally good at full-screen resolution on my new HD monitor as if I were watching the original PowerPoint.
Hope this helps both of you.