OK, I have xmms working now. The problem was corrupted .ogg files, of all things. I usually use grip on my Debian box to rip my CDs, and it looks as though there was a recent bug, either in it or in Debian's vorbis-tools, that created corrupt output files. I found out what was wrong when I installed vorbis-tools on the Z and ran ogginfo on one of the files, and it complained of a "hole in the data" (whatever that is) and a corrupted file. I had tried a couple of different ogg files on opie's xmms-embedded, but they were all recorded during the same period, and are all corrupt. They played ok on XMMS on my Debian box, too, and that just makes it all the more confusing.
Sigh.
Sorry to create a wild goose chase, folks. You did teach me a lot, though
opie-mediaplayer2 still crashes, though, even on known good oggfiles. I think I'll stick to xmms-embedded for now.
Thanks for your help,
.....Ron