I got Xubuntu to run, and it did play my music without stuttering. It did not run Opera, though. Also, after some flailing at the start, the panels did not show all the things they should, and there were not minimize, maximize or exit buttons on the windows. So I installed the Gnome-based standard Ubuntu package on top of Xubuntu. You can combine pretty much any *buntu. Apart from taking its sweet time, this went well enough. I also got to check that yes, the music still stutters under Gnome, though perhaps a little less than before, and Opera works. When I logged out of Gnome and into Xfce, the music did not stutter, programs ran faster (but I had to start them and close them twice) and Opera did not work.
Now to get Xubuntu to behave as expected. I partly got the panels back to their starting condition by deleting the config files. I still could not add various things to the panels despite the OS pretending to do so, such as a list of active windows. (Alt-tab for switching between windows did not work, don't know if expected to, works in Gnome.) Multitasking is not quite the same if you can only ever access the topmost window and must close it to access the next.
Eventually I came up with the idea to create a new user (well, it was recommended in one of the forum threads for a vaguely similar problem). So I did. At this point the user administration program hung for some minutes before responding again. There were no not two but zero users. Like all good Windows users, I did the rational thing: Logging out in a dignified manner and restarting the computer. Surprisingly, it did not start, did not even get to the login menu. It complained that it lacked a user called gdk (or some such, it was definitely not gkt as I first suspected).
Time to reinstall from the CD.