Many thanks for your help.
Ok, a couple of things. Firstly, was your solution designed to remove the infection, or just to make the files playable? I ask, because in fact they *are* already playable. They play normally, with no noticeable loss of quality. That is why I asked whether the infection is actually doing any harm in its current form, because if not I could leave the files alone, and just make sure I don't send them to anybody. If it did remove the infection, then it would certainly be worth pursuing, as I really don't want to lose some of these files.
(Incidentally, I tried to treat these as wma files and used a converter to change them back to mp3. When I did this the conversion worked, but the resultant files were very choppy and unusable.)
Secondly, I went through your procedure, and extracted the section from the registry. The only problem was that when I searched for my old user name, it is not there. I did find the new one, in one entry, but that was all
Once again, many thanks for the help.