Success (partial) at last!
It took a while, didn't it? Well, I had other things to do, and besides have another machine running W98, which I much prefer. I installed XP in another partition on the problem machine, so that I did have one instance of it, and ignored the problem until now. I was determined not to re-install in partition 1, because I knew all the stuff was still there (OK, so I could have copied it out, but that would have broken all the links). It is the test-and-learn machine, after all.
Anyway, I came upon another idea while browsing another forum without much hope; it was just a throwaway among much more technical stuff: "Have you tried using the PQboot rescue disk?" - I had, of course, without success; but the poster went on to say that Boot Magic must be installed on a Fat16 partition or the rescue disk wouldn't see it; however, if it was installed on a Fat32 partition, it could be detected by a rescue disk made under Windows 98 (convoluted, huh?).
My partitions are Fat32, so I took the rescue disk from my RELIABLE AND TRUSTY W98 machine, booted the XP one from it, and bingo! I was able to change to the first partition and boot into it. Truly magic. Black magic.
However, my troubles weren't over. My settings had disappeared - horrible green-and-blue wallpaper - and worse still, it wanted to re-authenticate. I had no internet connection at that point, so had to use the telephone method - is it laborious? - and after 6 tries I was into windows. All the programs were still installed, but no icons (a blessing: I hadn't managed to delete the IE one before).
Troubles are not quite over: Boot Magic hasn't shown itself, so I am still using the rescue disk to switch partitions. My shortcuts and things have all disappeared so I'll have to do them again ....
.... if I can be bothered. On the whole, I think I'll go with grub, after all that effort. As my favourite t-shirt says "Who needs Windows?"
Hope this helps.
Edna