Things may not be as bleak as I feared. Here's what Jerry Blinn just wrote regarding my problem:

Windows Media Player does absolutely nothing to AviSys files.

Since 1989, AviSys has used the extension .AVI for many of its data
files. In recent years Microsoft has begun using the .AVI extension
for some forms of media files. When seeing those AviSys files listed
in Windows (XP) Explorer, those files will have "Video Clip" icons
(or "AVI video" icons if you have another player as the
default). That means absolutely nothing, especially nothing to
AviSys -- it is simply an icon -- and has no impact on the file.

If one double-clicks one of those AviSys files (which nobody has any
reason to do unless they are just "playing around"), Windows Media
Player (or whatever program is set to run .AVI files, such as RealOne
Player) will start, examine the file, and either do nothing or will
report that the file is an invalid video file.

That's the extent of the issue -- either absolutely nothing or, if
"playing around," the file won't make any music. Period.

If Dennis has somehow lost data, he needs to talk to me. I'll
guarantee that if he has lost data, it's not simply because some
files have .AVI extensions -- there is something else going on in his
system, or something has been done that we don't understand now.

If Dennis has made backups, his data is perfectly safe.

Remember, thousands of users are running AviSys, with .AVI data
files, most of them running Windows XP, virtually all of them with
Windows Media Player installed.

This is the first time in the 9 years that there has been a Windows
version of AviSys, with these thousands of users, that I have heard
anybody even suggest he or she has lost data because of Windows Media
Player. I have had a few occasions where somebody thought they could
somehow look at their data by double-clicking one of those files, and
has complained that Windows Media Player wouldn't play it!!!!

________________________________________________________________

Dennis Rockwell
Kennewick, WA
denrockwell at surfbest.net