So, failing to get a decent performance out of my 8GB Ubuntu partition, I completely reformatted it and installed Xubuntu, the smallest and lightest of the Ubuntu family, made for even older and slower machines than mine. Also I hoped that a brand new install would not contain any bugs that may have accumulated through two years and some months of Ubunting. This may or may not have worked as intended, but it quickly developed a bug of its own. After I let the updater install all recommended updates, the next session dawned without any of the panels or menus (like menu bar and task bar and system tray). I still had access to the file system, but lost this while desperately trying to get the menus back. No, simply logging out without saving the session and logging back in with xfce did not work. I tried the advice of a thread in the Ubuntu forums from 2007, to no avail. Finally I found another bug report where the current name of the panel process was written, and combined it with the old thread. Victory!
I inserted a CD, which caused the file handler to wake up. (There was no other way - I had foolishly disabled right-clicking on the desktop.) I then selected "desktop" as location and "open terminal". In the terminal window, I started the panel process
then logged out, making sure to mark the session as remember for next time. So far it seems to work. Also, so far the music plays happily and does not skip a beat even while the system opens programs, copies files and installs. That was definitely not the case before. Unfortunately it seems Xubuntu does not support Opera, or perhaps my installation is still slightly borked. Actually, it is slightly borked: The buttons for expanding, restoring, minimizing and closing windows are missing on all windows. But that may be a different bork from the problems with Opera. More investigation needed!